diff --git a/api/Browser.md b/api/Browser.md
index 46135cc0..58e56698 100644
--- a/api/Browser.md
+++ b/api/Browser.md
@@ -5,8 +5,18 @@
 
 Remember to free all browser references for the browser to shut down cleanly.
 Otherwise data such as cookies or other storage might not be flushed to disk
-when closing app, and other issues might occur as well. To free a reference
-just assign a None value to a "browser" variable.
+when closing app, and other issues might occur as well. If you store
+a reference to Frame somewhere in your code then to free it just assign
+a None value to the variable.
+
+To compare browser objects always use [GetIdentifier()](#getidentifier)
+method. Do not compare two Browser objects variables directly. There
+are some edge cases when after the OnBeforeClose event browser objects
+are no more globally referenced thus a new instance is created that
+wraps upstream CefBrowser object. Browser objects that were globally
+unreferenced do not have properties of the original Browser object,
+for example they do not have client callbacks, javascript bindings
+or user data set.
 
 
 Table of contents:
diff --git a/api/Frame.md b/api/Frame.md
index f214bdcd..aef391b4 100644
--- a/api/Frame.md
+++ b/api/Frame.md
@@ -3,6 +3,19 @@
 
 # Frame (object)
 
+Remember to free all frame references for the browser to shut down cleanly.
+Otherwise data such as cookies or other storage might not be flushed to disk
+when closing app, and other issues might occur as well. If you store
+a reference to Frame somewhere in your code then to free it just assign
+a None value to the variable.
+
+To compare frame objects always use [GetIdentifier()](#getidentifier)
+method. Do not compare two Frame objects variables directly. There
+are some edge cases when after the OnBeforeClose event frame objects
+are no more globally referenced thus a new instance is created that
+wraps upstream CefFrame object. Frame objects that were globally
+unreferenced do not have properties of the original Frame object.
+
 
 Table of contents:
 * [Methods](#methods)
diff --git a/api/JavascriptCallback.md b/api/JavascriptCallback.md
index 6f4ba790..97b3bc06 100644
--- a/api/JavascriptCallback.md
+++ b/api/JavascriptCallback.md
@@ -15,7 +15,9 @@ See also [Issue #11](../issues/11) (Throw JS / Python exceptions according to ex
 Table of contents:
 * [Methods](#methods)
   * [Call](#call)
-  * [GetName](#getname)
+  * [GetFrame](#getframe)
+  * [GetId](#getid)
+  * [GetFunctionName](#getfunctionname)
 
 
 ## Methods
@@ -30,10 +32,29 @@ Table of contents:
 
 Call the javascript callback function.
 
-For a list of allowed types for `mixed` see [JavascriptBindings](JavascriptBindings.md).IsValueAllowed().
+For a list of allowed types for `mixed` see JavascriptBindings.[IsValueAllowed()](JavascriptBindings.md#isvalueallowed).
 
 
-### GetName
+### GetFrame
+
+| | |
+| --- | --- |
+| __Return__ | [Frame](Frame.md) |
+
+Get Frame object associated with this callback. If Browser was destroyed
+then Frame may be None.
+
+
+### GetId
+
+| | |
+| --- | --- |
+| __Return__ | int |
+
+Get this callback's identifier.
+
+
+### GetFunctionName
 
 | | |
 | --- | --- |
diff --git a/src/browser.pyx b/src/browser.pyx
index c5aadd53..d27a75e7 100644
--- a/src/browser.pyx
+++ b/src/browser.pyx
@@ -17,75 +17,109 @@ MOUSEBUTTON_RIGHT = cef_types.MBT_RIGHT
 # get segmentation faults, as they will be garbage collected.
 
 cdef dict g_pyBrowsers = {}
+
+# Unreferenced browsers are added to this list in OnBeforeClose().
+# Must keep a list of unreferenced browsers so that a new reference
+# is not created in GetPyBrowser() when browser was closed.
+cdef list g_unreferenced_browsers = []  # [int identifier, ..]
+
+# Browsers that are about to be closed are added to this list in
+# CloseBrowser().
 cdef list g_closed_browsers = []  # [int identifier, ..]
 
 cdef PyBrowser GetPyBrowserById(int browserId):
+    """May return None value so always check returned value."""
     if browserId in g_pyBrowsers:
         return g_pyBrowsers[browserId]
     return None
 
-cdef PyBrowser GetPyBrowser(CefRefPtr[CefBrowser] cefBrowser):
+cdef PyBrowser GetPyBrowser(CefRefPtr[CefBrowser] cefBrowser,
+                                    callerIdStr="GetPyBrowser"):
+    """The second argument 'callerIdStr' is so that a debug
+    message can be displayed informing which CEF handler callback
+    is being called to which an incomplete PyBrowser instance is
+    provided."""
+
     global g_pyBrowsers
+
+    # This probably ain't needed, but just to be sure.
     if <void*>cefBrowser == NULL or not cefBrowser.get():
-        # noinspection PyUnresolvedReferences
-        Debug("GetPyBrowser(): returning None")
-        return None
+        raise Exception("{caller}: CefBrowser reference is NULL"
+                        .format(caller=callerIdStr))
 
     cdef PyBrowser pyBrowser
     cdef int browserId
-    cdef int identifier
-
     browserId = cefBrowser.get().GetIdentifier()
+
     if browserId in g_pyBrowsers:
         return g_pyBrowsers[browserId]
 
+    # This code probably ain't needed.
+    # ----
+    cdef list toRemove = []
+    cdef int identifier
     for identifier, pyBrowser in g_pyBrowsers.items():
         if not pyBrowser.cefBrowser.get():
-            # noinspection PyUnresolvedReferences
-            Debug("GetPyBrowser(): removing an empty CefBrowser reference, "
-                  "browserId=%s" % identifier)
-            del g_pyBrowsers[identifier]
+            toRemove.append(identifier)
+    for identifier in toRemove:
+        Debug("GetPyBrowser(): removing an empty CefBrowser reference,"
+              " browserId=%s" % identifier)
+        RemovePyBrowser(identifier)
+    # ----
 
-    # noinspection PyUnresolvedReferences
-    Debug("GetPyBrowser(): creating new PyBrowser, browserId=%s" % browserId)
     pyBrowser = PyBrowser()
     pyBrowser.cefBrowser = cefBrowser
-    g_pyBrowsers[browserId] = pyBrowser
-
-    # Inherit client callbacks and javascript bindings
-    # from parent browser.
-
-    # Checking __outerWindowHandle as we should not inherit
-    # client callbacks and javascript bindings if the browser
-    # was created explicitily by calling CreateBrowserSync().
-
-    # Popups inherit client callbacks by default.
-
-    # Popups inherit javascript bindings only when "bindToPopups"
-    # constructor param was set to True.
 
     cdef WindowHandle openerHandle
     cdef dict clientCallbacks
     cdef JavascriptBindings javascriptBindings
     cdef PyBrowser tempPyBrowser
 
-    if pyBrowser.IsPopup() and \
-            not pyBrowser.GetUserData("__outerWindowHandle"):
-        openerHandle = pyBrowser.GetOpenerWindowHandle()
-        for identifier, tempPyBrowser in g_pyBrowsers.items():
-            if tempPyBrowser.GetWindowHandle() == openerHandle:
-                clientCallbacks = tempPyBrowser.GetClientCallbacksDict()
-                if clientCallbacks:
-                    pyBrowser.SetClientCallbacksDict(clientCallbacks)
-                javascriptBindings = tempPyBrowser.GetJavascriptBindings()
-                if javascriptBindings:
-                    if javascriptBindings.GetBindToPopups():
-                        pyBrowser.SetJavascriptBindings(javascriptBindings)
+    if browserId in g_unreferenced_browsers:
+        # This browser was already unreferenced due to OnBeforeClose
+        # was already called. An incomplete new instance of Browser
+        # object is created. This instance doesn't have the client
+        # callbacks, javascript bindings or user data that was already
+        # available in the original Browser object.
+        Debug("{caller}: Browser was already globally unreferenced"
+              ", a new incomplete instance is created, browser id={id}"
+              .format(caller=callerIdStr, id=str(browserId)))
+    else:
+        # This is first creation of browser. Store a reference globally
+        # and inherit client callbacks and javascript bindings from
+        # parent browsers.
+        Debug("GetPyBrowser(): create new PyBrowser, browserId=%s"
+              % browserId)
+
+        g_pyBrowsers[browserId] = pyBrowser
+
+        # Inherit client callbacks and javascript bindings
+        # from parent browser.
+        # - Checking __outerWindowHandle as we should not inherit
+        #   client callbacks and javascript bindings if the browser
+        #   was created explicitily by calling CreateBrowserSync().
+        # - Popups inherit client callbacks by default.
+        # - Popups inherit javascript bindings only when "bindToPopups"
+        #   constructor param was set to True.
+
+        if pyBrowser.IsPopup() and \
+                not pyBrowser.GetUserData("__outerWindowHandle"):
+            openerHandle = pyBrowser.GetOpenerWindowHandle()
+            for identifier, tempPyBrowser in g_pyBrowsers.items():
+                if tempPyBrowser.GetWindowHandle() == openerHandle:
+                    clientCallbacks = tempPyBrowser.GetClientCallbacksDict()
+                    if clientCallbacks:
+                        pyBrowser.SetClientCallbacksDict(clientCallbacks)
+                    javascriptBindings = tempPyBrowser.GetJavascriptBindings()
+                    if javascriptBindings:
+                        if javascriptBindings.GetBindToPopups():
+                            pyBrowser.SetJavascriptBindings(javascriptBindings)
+
     return pyBrowser
 
 cdef void RemovePyBrowser(int browserId) except *:
     # Called from LifespanHandler_OnBeforeClose().
-    global g_pyBrowsers
+    global g_pyBrowsers, g_unreferenced_browsers
     if browserId in g_pyBrowsers:
         if len(g_pyBrowsers) == 1:
             # This is the last browser remaining.
@@ -97,6 +131,7 @@ cdef void RemovePyBrowser(int browserId) except *:
         # noinspection PyUnresolvedReferences
         Debug("del g_pyBrowsers[%s]" % browserId)
         del g_pyBrowsers[browserId]
+        g_unreferenced_browsers.append(browserId)
     else:
         # noinspection PyUnresolvedReferences
         Debug("RemovePyBrowser() FAILED: browser not found, id = %s" \
@@ -116,7 +151,7 @@ cdef public void PyBrowser_ShowDevTools(CefRefPtr[CefBrowser] cefBrowser
     # Called from ClientHandler::OnContextMenuCommand
     cdef PyBrowser pyBrowser
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "ShowDevTools")
         pyBrowser.ShowDevTools()
     except:
         (exc_type, exc_value, exc_trace) = sys.exc_info()
diff --git a/src/cefpython.pyx b/src/cefpython.pyx
index 941fff00..6fb922e1 100644
--- a/src/cefpython.pyx
+++ b/src/cefpython.pyx
@@ -838,7 +838,8 @@ def CreateBrowserSync(windowInfo=None,
             requestContextHandler.get().SetBrowser(cefBrowser)
 
     cdef PyBrowser pyBrowser = GetPyBrowser(cefBrowser)
-    pyBrowser.SetUserData("__outerWindowHandle", int(windowInfo.parentWindowHandle))
+    pyBrowser.SetUserData("__outerWindowHandle",
+                          int(windowInfo.parentWindowHandle))
 
     return pyBrowser
 
@@ -889,6 +890,10 @@ def Shutdown():
     # Run some message loop work, force closing browsers and then run
     # some message loop work again for the browsers to close cleanly.
     #
+    # UPDATE: This code needs to be rechecked. There were enhancements
+    #         to unrferencing globally stored Browser objects in
+    #         g_pyBrowsers. See Issue #330 and its commits.
+    #
     # CASE 1:
     # There might be a case when python error occured after creating
     # browser, but before any message loop was run. In such case
diff --git a/src/frame.pyx b/src/frame.pyx
index 9a3faca9..9342719c 100644
--- a/src/frame.pyx
+++ b/src/frame.pyx
@@ -3,6 +3,7 @@
 # Project website: https://github.com/cztomczak/cefpython
 
 include "cefpython.pyx"
+include "browser.pyx"
 
 cdef dict g_pyFrames = {}
 
@@ -17,25 +18,51 @@ cdef PyFrame GetPyFrameById(int browserId, object frameId):
 
 cdef PyFrame GetPyFrame(CefRefPtr[CefFrame] cefFrame):
     global g_pyFrames
+
+    # This code probably ain't needed, but just to be sure.
     if <void*>cefFrame == NULL or not cefFrame.get():
-        Debug("GetPyFrame(): returning None")
-        return
+        raise Exception("GetPyFrame(): CefFrame reference is NULL")
+
     cdef PyFrame pyFrame
     cdef object frameId = cefFrame.get().GetIdentifier()  # int64
     cdef int browserId = cefFrame.get().GetBrowser().get().GetIdentifier()
     assert (frameId and browserId), "frameId or browserId empty"
     cdef object uniqueFrameId = GetUniqueFrameId(browserId, frameId)
+
     if uniqueFrameId in g_pyFrames:
         return g_pyFrames[uniqueFrameId]
+
+    # This code probably ain't needed.
+    # ----
+    cdef list toRemove = []
     for uFid, pyFrame in g_pyFrames.items():
         if not pyFrame.cefFrame.get():
-            Debug("GetPyFrame(): removing an empty CefFrame reference, " \
-                    "uniqueFrameId = %s" % uniqueFrameId)
-            del g_pyFrames[uFid]
-    # Debug("GetPyFrame(): creating new PyFrame, frameId=%s" % frameId)
+            toRemove.append(uFid)
+    for uFid in toRemove:
+        Debug("GetPyFrame(): removing an empty CefFrame reference, "
+              "uniqueFrameId = %s" % uniqueFrameId)
+        del g_pyFrames[uFid]
+    # ----
+
     pyFrame = PyFrame(browserId, frameId)
     pyFrame.cefFrame = cefFrame
-    g_pyFrames[uniqueFrameId] = pyFrame
+
+    if browserId in g_unreferenced_browsers:
+        # Browser was already globally unreferenced in OnBeforeClose,
+        # thus all frames are globally unreferenced too. Create a new
+        # incomplete instance of PyFrame object. Read comments in
+        # browser.pyx > GetPyBrowser and in Browser.md for what
+        # "incomplete" means.
+        pass
+    else:
+        # Keep a global reference to this frame only if the browser
+        # wasn't destroyed in OnBeforeClose. Otherwise we would leave
+        # dead frames references living forever.
+        # SIDE EFFECT: two calls to GetPyFrame for the same frame object
+        #              may return two different PyFrame objects. Compare
+        #              frame objects always using GetIdentifier().
+        # Debug("GetPyFrame(): create new PyFrame, frameId=%s" % frameId)
+        g_pyFrames[uniqueFrameId] = pyFrame
     return pyFrame
 
 cdef void RemovePyFrame(int browserId, object frameId) except *:
diff --git a/src/handlers/display_handler.pyx b/src/handlers/display_handler.pyx
index 3db61a7c..d67cb4d1 100644
--- a/src/handlers/display_handler.pyx
+++ b/src/handlers/display_handler.pyx
@@ -3,6 +3,7 @@
 # Project website: https://github.com/cztomczak/cefpython
 
 include "../cefpython.pyx"
+include "../browser.pyx"
 
 cdef public void DisplayHandler_OnAddressChange(
         CefRefPtr[CefBrowser] cefBrowser,
@@ -14,7 +15,7 @@ cdef public void DisplayHandler_OnAddressChange(
     cdef py_string pyUrl
     cdef object callback
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnAddressChange")
         pyFrame = GetPyFrame(cefFrame)
         pyUrl = CefToPyString(cefUrl)
         callback = pyBrowser.GetClientCallback("OnAddressChange")
@@ -32,7 +33,7 @@ cdef public void DisplayHandler_OnTitleChange(
     cdef py_string pyTitle
     cdef object callback
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnTitleChange")
         pyTitle = CefToPyString(cefTitle)
         callback = pyBrowser.GetClientCallback("OnTitleChange")
         if callback:
@@ -51,7 +52,7 @@ cdef public cpp_bool DisplayHandler_OnTooltip(
     cdef object callback
     cdef py_bool returnValue
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnTooltip")
         pyText = CefToPyString(cefText)
         pyTextOut = [pyText]
         callback = pyBrowser.GetClientCallback("OnTooltip")
@@ -73,7 +74,7 @@ cdef public void DisplayHandler_OnStatusMessage(
     cdef py_string pyValue
     cdef object callback
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnStatusMessage")
         pyValue = CefToPyString(cefValue)
         callback = pyBrowser.GetClientCallback("OnStatusMessage")
         if callback:
@@ -94,7 +95,7 @@ cdef public cpp_bool DisplayHandler_OnConsoleMessage(
     cdef py_bool returnValue
     cdef object callback
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnConsoleMessage")
         pyMessage = CefToPyString(cefMessage)
         pySource = CefToPyString(cefSource)
         callback = pyBrowser.GetClientCallback("OnConsoleMessage")
diff --git a/src/handlers/focus_handler.pyx b/src/handlers/focus_handler.pyx
index f966c613..71c04523 100644
--- a/src/handlers/focus_handler.pyx
+++ b/src/handlers/focus_handler.pyx
@@ -3,6 +3,8 @@
 # Project website: https://github.com/cztomczak/cefpython
 
 include "../cefpython.pyx"
+include "../browser.pyx"
+
 cimport cef_types
 from cef_types cimport TID_UI
 
@@ -17,7 +19,7 @@ cdef public void FocusHandler_OnTakeFocus(
     cdef PyBrowser browser
     try:
         assert IsThread(TID_UI), "Must be called on the UI thread"
-        browser = GetPyBrowser(cef_browser)
+        browser = GetPyBrowser(cef_browser, "OnTakeFocus")
         callback = browser.GetClientCallback("OnTakeFocus")
         if callback:
             callback(browser=browser, next=next_)
@@ -34,7 +36,7 @@ cdef public cpp_bool FocusHandler_OnSetFocus(
     cdef py_bool ret
     try:
         assert IsThread(TID_UI), "Must be called on the UI thread"
-        browser = GetPyBrowser(cef_browser)
+        browser = GetPyBrowser(cef_browser, "OnSetFocus")
         callback = browser.GetClientCallback("OnSetFocus")
         if callback:
             ret = callback(browser=browser, source=source)
@@ -52,7 +54,7 @@ cdef public void FocusHandler_OnGotFocus(
     cdef PyBrowser browser
     try:
         assert IsThread(TID_UI), "Must be called on the UI thread"
-        browser = GetPyBrowser(cef_browser)
+        browser = GetPyBrowser(cef_browser, "OnGotFocus")
         callback = browser.GetClientCallback("OnGotFocus")
         if callback:
             callback(browser=browser)
diff --git a/src/handlers/javascript_dialog_handler.pyx b/src/handlers/javascript_dialog_handler.pyx
index 0c7fa071..283aad54 100644
--- a/src/handlers/javascript_dialog_handler.pyx
+++ b/src/handlers/javascript_dialog_handler.pyx
@@ -3,6 +3,7 @@
 # Project website: https://github.com/cztomczak/cefpython
 
 include "../cefpython.pyx"
+include "../browser.pyx"
 
 # enum cef_jsdialog_type_t
 cimport cef_types
@@ -48,7 +49,7 @@ cdef public cpp_bool JavascriptDialogHandler_OnJavascriptDialog(
     cdef object clientCallback
     cdef py_bool returnValue
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnJavascriptDialog")
         pyOriginUrl = CefToPyString(origin_url)
         pyMessageText = CefToPyString(message_text)
         pyDefaultPromptText = CefToPyString(default_prompt_text)
@@ -86,7 +87,8 @@ cdef public cpp_bool JavascriptDialogHandler_OnBeforeUnloadJavascriptDialog(
     cdef object clientCallback
     cdef py_bool returnValue
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser,
+                                         "OnBeforeUnloadJavascriptDialog")
         pyMessageText = CefToPyString(message_text)
         pyIsReload = bool(is_reload)
         pyCallback = CreatePyJavascriptDialogCallback(callback)
@@ -110,7 +112,8 @@ cdef public void JavascriptDialogHandler_OnResetJavascriptDialogState(
         ) except * with gil:
     cdef PyBrowser pyBrowser
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser,
+                                         "OnResetJavascriptDialogState")
         callback = pyBrowser.GetClientCallback(
                 "OnResetJavascriptDialogState")
         if callback:
@@ -124,7 +127,8 @@ cdef public void JavascriptDialogHandler_OnJavascriptDialogClosed(
         ) except * with gil:
     cdef PyBrowser pyBrowser
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser,
+                                         "OnJavascriptDialogClosed")
         callback = pyBrowser.GetClientCallback("OnJavascriptDialogClosed")
         if callback:
             callback(browser=pyBrowser)
diff --git a/src/handlers/keyboard_handler.pyx b/src/handlers/keyboard_handler.pyx
index 408487c5..c895b9b5 100644
--- a/src/handlers/keyboard_handler.pyx
+++ b/src/handlers/keyboard_handler.pyx
@@ -54,7 +54,7 @@ cdef public cpp_bool KeyboardHandler_OnPreKeyEvent(
     cdef py_bool returnValue
     cdef object callback
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnPreKeyEvent")
         pyEvent = CefToPyKeyEvent(cefEvent)
         pyIsKeyboardShortcutOut = [cefIsKeyboardShortcut[0]]
         callback = pyBrowser.GetClientCallback("OnPreKeyEvent")
@@ -82,7 +82,7 @@ cdef public cpp_bool KeyboardHandler_OnKeyEvent(
     cdef py_bool returnValue
     cdef object callback
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnKeyEvent")
         pyEvent = CefToPyKeyEvent(cefEvent)
         callback = pyBrowser.GetClientCallback("OnKeyEvent")
         if callback:
diff --git a/src/handlers/lifespan_handler.pyx b/src/handlers/lifespan_handler.pyx
index dbc37943..ad6730b1 100644
--- a/src/handlers/lifespan_handler.pyx
+++ b/src/handlers/lifespan_handler.pyx
@@ -47,7 +47,7 @@ cdef public cpp_bool LifespanHandler_OnBeforePopup(
     cdef object callback
     cdef py_bool returnValue
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnBeforePopup")
         pyFrame = GetPyFrame(cefFrame)
         pyTargetUrl = CefToPyString(targetUrl)
         pyTargetFrameName = CefToPyString(targetFrameName)
@@ -84,7 +84,7 @@ cdef public void LifespanHandler_OnAfterCreated(
         ) except * with gil:
     cdef PyBrowser pyBrowser
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnAfterCreated")
         callback = GetGlobalClientCallback("OnAfterCreated")
         if callback:
             callback(browser=pyBrowser)
@@ -97,7 +97,7 @@ cdef public cpp_bool LifespanHandler_DoClose(
         ) except * with gil:
     cdef PyBrowser pyBrowser
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "DoClose")
         callback = pyBrowser.GetClientCallback("DoClose")
         if callback:
             return bool(callback(browser=pyBrowser))
@@ -112,7 +112,8 @@ cdef public void LifespanHandler_OnBeforeClose(
     cdef PyBrowser pyBrowser
     cdef object callback
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        Debug("LifespanHandler_OnBeforeClose")
+        pyBrowser = GetPyBrowser(cefBrowser, "OnBeforeClose")
         callback = pyBrowser.GetClientCallback("OnBeforeClose")
         if callback:
             callback(browser=pyBrowser)
@@ -120,6 +121,8 @@ cdef public void LifespanHandler_OnBeforeClose(
         RemovePyFramesForBrowser(pyBrowser.GetIdentifier())
         RemovePyBrowser(pyBrowser.GetIdentifier())
         if g_MessageLoop_called and not len(g_pyBrowsers):
+            # Automatically quit message loop when last browser was closed.
+            # This is required for hello_world.py example to work.
             QuitMessageLoop()
 
     except:
diff --git a/src/handlers/load_handler.pyx b/src/handlers/load_handler.pyx
index 47e1d28d..c7627f5c 100644
--- a/src/handlers/load_handler.pyx
+++ b/src/handlers/load_handler.pyx
@@ -3,6 +3,7 @@
 # Project website: https://github.com/cztomczak/cefpython
 
 include "../cefpython.pyx"
+include "../browser.pyx"
 
 cdef public void LoadHandler_OnLoadingStateChange(
         CefRefPtr[CefBrowser] cefBrowser,
@@ -13,7 +14,7 @@ cdef public void LoadHandler_OnLoadingStateChange(
     cdef PyBrowser pyBrowser
     cdef object callback
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnLoadingStateChange")
         callback = pyBrowser.GetClientCallback("OnLoadingStateChange")
         if callback:
             callback(browser=pyBrowser,
@@ -32,7 +33,7 @@ cdef public void LoadHandler_OnLoadStart(
     cdef PyFrame pyFrame
     cdef object clientCallback
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnLoadStart")
         pyFrame = GetPyFrame(cefFrame)
         clientCallback = pyBrowser.GetClientCallback("OnLoadStart")
         if clientCallback:
@@ -50,7 +51,7 @@ cdef public void LoadHandler_OnLoadEnd(
     cdef PyFrame pyFrame
     cdef object clientCallback
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnLoadEnd")
         pyFrame = GetPyFrame(cefFrame)
         clientCallback = pyBrowser.GetClientCallback("OnLoadEnd")
         if clientCallback:
@@ -77,7 +78,7 @@ cdef public void LoadHandler_OnLoadError(
         # the error code will be ERR_ABORTED. In such cases calls
         # to OnLoadError should be ignored and not handled by user
         # scripts. The wxpython example implements such behavior.
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnLoadError")
         pyFrame = GetPyFrame(cefFrame)
         errorTextOut = [CefToPyString(cefErrorText)]
         clientCallback = pyBrowser.GetClientCallback("OnLoadError")
diff --git a/src/handlers/render_handler.pyx b/src/handlers/render_handler.pyx
index acbb5c28..1594d6bd 100644
--- a/src/handlers/render_handler.pyx
+++ b/src/handlers/render_handler.pyx
@@ -3,6 +3,7 @@
 # Project website: https://github.com/cztomczak/cefpython
 
 include "../cefpython.pyx"
+include "../browser.pyx"
 
 cimport cef_types
 
@@ -29,7 +30,7 @@ cdef public cpp_bool RenderHandler_GetRootScreenRect(
     cdef list pyRect = []
     cdef py_bool ret
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "GetRootScreenRect")
         callback = pyBrowser.GetClientCallback("GetRootScreenRect")
         if callback:
             ret = callback(browser=pyBrowser, rect_out=pyRect)
@@ -56,7 +57,7 @@ cdef public cpp_bool RenderHandler_GetViewRect(
     cdef list pyRect = []
     cdef py_bool ret
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "GetViewRect")
         callback = pyBrowser.GetClientCallback("GetViewRect")
         if callback:
             ret = callback(browser=pyBrowser, rect_out=pyRect)
@@ -83,7 +84,7 @@ cdef public cpp_bool RenderHandler_GetScreenRect(
     cdef list pyRect = []
     cdef py_bool ret
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "GetScreenRect")
         callback = pyBrowser.GetClientCallback("GetScreenRect")
         if callback:
             ret = callback(browser=pyBrowser, rect_out=pyRect)
@@ -112,7 +113,7 @@ cdef public cpp_bool RenderHandler_GetScreenPoint(
     cdef list screenCoordinates = []
     cdef py_bool ret
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "GetScreenPoint")
         callback = pyBrowser.GetClientCallback("GetScreenPoint")
         if callback:
             ret = callback(browser=pyBrowser,
@@ -146,7 +147,7 @@ cdef public void RenderHandler_OnPopupShow(
         ) except * with gil:
     cdef PyBrowser pyBrowser
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnPopupShow")
         callback = pyBrowser.GetClientCallback("OnPopupShow")
         if callback:
             callback(browser=pyBrowser, show=show)
@@ -161,7 +162,7 @@ cdef public void RenderHandler_OnPopupSize(
     cdef PyBrowser pyBrowser
     cdef list pyRect
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnPopupSize")
         callback = pyBrowser.GetClientCallback("OnPopupSize")
         if callback:
             pyRect = [cefRect.x, cefRect.y, cefRect.width, cefRect.height]
@@ -187,8 +188,7 @@ cdef public void RenderHandler_OnPaint(
     cdef CefRect cefRect
     cdef PaintBuffer paintBuffer
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
-
+        pyBrowser = GetPyBrowser(cefBrowser, "OnPaint")
         iterator = cefDirtyRects.begin()
         while iterator != cefDirtyRects.end():
             cefRect = deref(iterator)
@@ -223,7 +223,7 @@ cdef public void RenderHandler_OnCursorChange(
         ) except * with gil:
     cdef PyBrowser pyBrowser
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnCursorChange")
         callback = pyBrowser.GetClientCallback("OnCursorChange")
         if callback:
             callback(browser=pyBrowser, cursor=<uintptr_t>cursor)
@@ -236,7 +236,7 @@ cdef public void RenderHandler_OnScrollOffsetChanged(
         ) except * with gil:
     cdef PyBrowser pyBrowser
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnScrollOffsetChanged")
         callback = pyBrowser.GetClientCallback("OnScrollOffsetChanged")
         if callback:
             callback(browser=pyBrowser)
@@ -254,7 +254,7 @@ cdef public cpp_bool RenderHandler_StartDragging(
     cdef DragData drag_data
     cdef py_bool ret
     try:
-        browser = GetPyBrowser(cef_browser)
+        browser = GetPyBrowser(cef_browser, "StartDragging")
         drag_data = DragData_Init(cef_drag_data)
         callback = browser.GetClientCallback("StartDragging")
         if callback:
@@ -280,7 +280,7 @@ cdef public void RenderHandler_UpdateDragCursor(
         ) except * with gil:
     cdef PyBrowser browser
     try:
-        browser = GetPyBrowser(cef_browser)
+        browser = GetPyBrowser(cef_browser, "UpdateDragCursor")
         callback = browser.GetClientCallback("UpdateDragCursor")
         if callback:
             callback(browser=browser, operation=operation)
diff --git a/src/handlers/request_handler.pyx b/src/handlers/request_handler.pyx
index 259e23a1..b2cadbe7 100644
--- a/src/handlers/request_handler.pyx
+++ b/src/handlers/request_handler.pyx
@@ -3,6 +3,7 @@
 # Project website: https://github.com/cztomczak/cefpython
 
 include "../cefpython.pyx"
+include "../browser.pyx"
 
 # cef_termination_status_t
 cimport cef_types
@@ -67,7 +68,7 @@ cdef public cpp_bool RequestHandler_OnBeforeBrowse(
     cdef object clientCallback
     cdef py_bool returnValue
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnBeforeBrowse")
         pyFrame = GetPyFrame(cefFrame)
         pyRequest = CreatePyRequest(cefRequest)
         pyIsRedirect = bool(cefIsRedirect)
@@ -97,7 +98,7 @@ cdef public cpp_bool RequestHandler_OnBeforeResourceLoad(
     cdef object clientCallback
     cdef py_bool returnValue
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnBeforeResourceLoad")
         pyFrame = GetPyFrame(cefFrame)
         pyRequest = CreatePyRequest(cefRequest)
         clientCallback = pyBrowser.GetClientCallback("OnBeforeResourceLoad")
@@ -125,7 +126,7 @@ cdef public CefRefPtr[CefResourceHandler] RequestHandler_GetResourceHandler(
     cdef object clientCallback
     cdef object returnValue
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "GetResourceHandler")
         pyFrame = GetPyFrame(cefFrame)
         pyRequest = CreatePyRequest(cefRequest)
         clientCallback = pyBrowser.GetClientCallback("GetResourceHandler")
@@ -161,7 +162,7 @@ cdef public void RequestHandler_OnResourceRedirect(
     cdef PyResponse pyResponse
     cdef object clientCallback
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnResourceRedirect")
         pyFrame = GetPyFrame(cefFrame)
         pyOldUrl = CefToPyString(cefOldUrl)
         pyNewUrlOut = [CefToPyString(cefNewUrl)]
@@ -206,7 +207,7 @@ cdef public cpp_bool RequestHandler_GetAuthCredentials(
     cdef list pyPasswordOut
     cdef object clientCallback
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "GetAuthCredentials")
         pyFrame = GetPyFrame(cefFrame)
         pyIsProxy = bool(cefIsProxy)
         pyHost = CefToPyString(cefHost)
@@ -260,7 +261,7 @@ cdef public cpp_bool RequestHandler_OnQuotaRequest(
     cdef py_bool returnValue
     cdef object clientCallback
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnQuotaRequest")
         pyOriginUrl = CefToPyString(cefOriginUrl)
         clientCallback = pyBrowser.GetClientCallback("OnQuotaRequest")
         if clientCallback:
@@ -290,7 +291,7 @@ cdef public CefRefPtr[CefCookieManager] RequestHandler_GetCookieManager(
     cdef object clientCallback
     cdef PyCookieManager returnValue
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "GetCookieManager")
         pyMainUrl = CefToPyString(cefMainUrl)
         if pyBrowser:
             # Browser may be empty.
@@ -322,7 +323,7 @@ cdef public void RequestHandler_OnProtocolExecution(
     cdef list pyAllowOSExecutionOut
     cdef object clientCallback
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnProtocolExecution")
         pyUrl = CefToPyString(cefUrl)
         pyAllowOSExecutionOut = [bool(cefAllowOSExecution)]
         clientCallback = pyBrowser.GetClientCallback("OnProtocolExecution")
@@ -357,7 +358,7 @@ cdef public cpp_bool RequestHandler_OnBeforePluginLoad(
     cdef py_bool returnValue
     cdef object clientCallback
     try:
-        py_browser = GetPyBrowser(browser)
+        py_browser = GetPyBrowser(browser, "OnBeforePluginLoad")
         py_plugin_info = CreatePyWebPluginInfo(plugin_info)
         clientCallback = GetGlobalClientCallback("OnBeforePluginLoad")
         if clientCallback:
@@ -412,7 +413,7 @@ cdef public void RequestHandler_OnRendererProcessTerminated(
     cdef PyBrowser pyBrowser
     cdef object clientCallback
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnRendererProcessTerminated")
         clientCallback = pyBrowser.GetClientCallback(
                 "OnRendererProcessTerminated")
         if clientCallback:
@@ -434,7 +435,7 @@ cdef public void RequestHandler_OnPluginCrashed(
     cdef PyBrowser pyBrowser
     cdef object clientCallback
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnPluginCrashed")
         clientCallback = pyBrowser.GetClientCallback("OnPluginCrashed")
         if clientCallback:
             clientCallback(
diff --git a/src/handlers/v8context_handler.pyx b/src/handlers/v8context_handler.pyx
index 741daab8..704f6ad9 100644
--- a/src/handlers/v8context_handler.pyx
+++ b/src/handlers/v8context_handler.pyx
@@ -9,6 +9,7 @@
 # a bit delayed due to asynchronous way this is being done.
 
 include "../cefpython.pyx"
+include "../browser.pyx"
 
 cdef public void V8ContextHandler_OnContextCreated(
         CefRefPtr[CefBrowser] cefBrowser,
@@ -19,7 +20,7 @@ cdef public void V8ContextHandler_OnContextCreated(
     cdef object clientCallback
     try:
         Debug("V8ContextHandler_OnContextCreated()")
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "OnContextCreated")
         pyBrowser.SetUserData("__v8ContextCreated", True)
         pyFrame = GetPyFrame(cefFrame)
         # User defined callback.
@@ -48,6 +49,10 @@ cdef public void V8ContextHandler_OnContextReleased(
         # were released.
         Debug("V8ContextHandler_OnContextReleased()")
         pyBrowser = GetPyBrowserById(browserId)
+        if not pyBrowser:
+            Debug("OnContextReleased: Browser doesn't exist anymore, id={id}"
+                  .format(id=str(browserId)))
+            return
         pyFrame = GetPyFrameById(browserId, frameId)
         if pyBrowser and pyFrame:
             clientCallback = pyBrowser.GetClientCallback("OnContextReleased")
@@ -56,10 +61,10 @@ cdef public void V8ContextHandler_OnContextReleased(
         else:
             if not pyBrowser:
                 Debug("V8ContextHandler_OnContextReleased() WARNING: "
-                        "pyBrowser not found")
+                        "PyBrowser not found")
             if not pyFrame:
                 Debug("V8ContextHandler_OnContextReleased() WARNING: "
-                        "pyFrame not found")
+                        "PyFrame not found")
         RemovePyFrame(browserId, frameId)
     except:
         (exc_type, exc_value, exc_trace) = sys.exc_info()
diff --git a/src/handlers/v8function_handler.pyx b/src/handlers/v8function_handler.pyx
index c4cfd89d..2c9b3f1c 100644
--- a/src/handlers/v8function_handler.pyx
+++ b/src/handlers/v8function_handler.pyx
@@ -3,6 +3,7 @@
 # Project website: https://github.com/cztomczak/cefpython
 
 include "../cefpython.pyx"
+include "../browser.pyx"
 
 cdef public void V8FunctionHandler_Execute(
         CefRefPtr[CefBrowser] cefBrowser,
@@ -18,7 +19,7 @@ cdef public void V8FunctionHandler_Execute(
     cdef object returnValue
     cdef py_string jsErrorMessage
     try:
-        pyBrowser = GetPyBrowser(cefBrowser)
+        pyBrowser = GetPyBrowser(cefBrowser, "V8FunctionHandler_Execute")
         pyFrame = GetPyFrame(cefFrame)
         functionName = CefToPyString(cefFunctionName)
         Debug("V8FunctionHandler_Execute(): functionName=%s" % functionName)
diff --git a/src/javascript_callback.pyx b/src/javascript_callback.pyx
index 81a06eb8..be474be7 100644
--- a/src/javascript_callback.pyx
+++ b/src/javascript_callback.pyx
@@ -3,9 +3,11 @@
 # Project website: https://github.com/cztomczak/cefpython
 
 include "cefpython.pyx"
+include "browser.pyx"
 
 cdef JavascriptCallback CreateJavascriptCallback(int callbackId,
-        CefRefPtr[CefBrowser] cefBrowser, object frameId, py_string functionName):
+        CefRefPtr[CefBrowser] cefBrowser, object frameId,
+        py_string functionName):
     # frameId is int64
     cdef JavascriptCallback jsCallback = JavascriptCallback()
     jsCallback.callbackId = callbackId
@@ -17,6 +19,8 @@ cdef JavascriptCallback CreateJavascriptCallback(int callbackId,
     return jsCallback
 
 cdef class JavascriptCallback:
+    """A javascript callback object may still live while browser/frame
+    are destroyed. Always check frame/browser for None value."""
     cdef int callbackId
     cdef PyFrame frame
     cdef py_string functionName
@@ -32,18 +36,24 @@ cdef class JavascriptCallback:
                         "ExecuteJavascriptCallback",
                         [self.callbackId] + list(args))
             else:
-                Debug("JavascriptCallback.Call() FAILED: browser not found, " \
-                        "callbackId = %s" % self.callbackId)
+                # This code probably ain't needed
+                raise Exception("JavascriptCallback.Call() FAILED: browser"
+                                " not found, callbackId = %s"
+                                % self.callbackId)
         else:
-            Debug("JavascriptCallback.Call() FAILED: frame not found, " \
-                    "callbackId = %s" % self.callbackId)
+            # This code probably ain't needed
+            raise Exception("JavascriptCallback.Call() FAILED: frame not found"
+                            ", callbackId = %s" % self.callbackId)
 
     def GetFunctionName(self):
         return self.functionName
 
     def GetName(self):
-        # DEPRECATED name.
+        """@deprecated."""
         return self.GetFunctionName()
 
+    def GetId(self):
+        return self.callbackId
+
     def GetFrame(self):
         return self.frame
diff --git a/tools/build.py b/tools/build.py
index fce02f34..9b6db351 100644
--- a/tools/build.py
+++ b/tools/build.py
@@ -184,6 +184,17 @@ def check_directories():
     if not os.path.exists(BUILD_CEFPYTHON):
         os.makedirs(BUILD_CEFPYTHON)
 
+    # Info if directory missing
+    if not os.path.exists(CEF_BINARIES_LIBRARIES):
+        prebuilt_name = get_cef_binaries_libraries_basename(OS_POSTFIX2)
+        print("[build.py] ERROR: Couldn't find CEF prebuilt binaries and"
+              " libraries: 'build/{prebuilt_dir}/'. Download it"
+              " from GitHub released tagged eg. 'v50-upstream` or download"
+              " CEF binaries from Spotify Automated Builds and then run"
+              "`automate.py --prebuilt-cef`."
+              .format(prebuilt_dir=prebuilt_name))
+        sys.exit(1)
+
     # Check directories exist
     assert os.path.exists(BUILD_DIR)
     assert os.path.exists(BUILD_CEFPYTHON)