Problematic extensions

This article lists some of the extensions that are known to cause unwanted side effects in Firefox or in other extensions and plugins, along with recommended workarounds. There are hundreds of extensions, and this list is not updated systematically. In addition, extensions can cause problems in combination with each other. As a result, only a few well-known problems are listed here. An extension can still cause a problem even if it is not listed. If you do not find the problem here, start Firefox in Safe Mode to disable all extensions, or follow the steps outlined in the Standard diagnostic - Firefox article.

Extensions

Extension	Versions affected	Problem	Workaround	References
A9 Toolbar	All	Causes "Unresponsive script" dialog	Uninstall A9 Toolbar	[1]
Adblock	All	Having the OBJ_TABS setting enabled has been known to interfere with the ActiveX plugin (if installed). It can cause the plugin to ignore its configuration and run any ActiveX control, instead of the controls it is restricted to. Such a situation could potentially be a big security risk.	If you have the ActiveX plugin, keep the Adblock OBJ_TABS setting disabled, or update to Firefox 1.5.0.7 or later versions, which include a fix.	[2] [3]
		Having the OBJ_TABS setting enabled will interfere with the Java plugin. Java applets will not display unless this setting is disabled.	If you want Java applets to display, keep the Adblock OBJ_TABS setting disabled.	[4][5]
		Having the OBJ_TABS setting enabled may interfere with the Flash Player 8.0 plugin. No Flash content will be displayed unless this setting is disabled.	If updating to Adblock 0.5.3.042 or later does not resolve the issue, keep the Adblock OBJ_TABS setting disabled.	[6]
		Having the OBJ_TABS setting enabled may interfere with the Windows Media Player plugin. Player video and controls will not appear on page, but sometimes audio will still play.	If updating to Adblock 0.5.3.042 or later does not resolve the issue, keep the Adblock OBJ_TABS setting disabled.	[7]
		Causes Google Gmail Chat to crash.	?	[8]
	Prior to 0.5.3.042	Having the OBJ_TABS setting enabled interferes with the Quicktime plugin. Video playback will have sound but no video.	Update to Adblock 0.5.3.042 or later.	[9] [10]
	Prior to 0.5.3.042	Causes Firefox to hog memory	Update to Adblock 0.5.3.042 or later.	[11]
	0.5.2.039	(Firefox 1.0.x) Tools -> Extensions window won't open after using "de-install" in the Adblock options menu.	Adblock should be uninstalled in Firefox from the Tools -> Extensions window (start in Firefox Safe Mode if the Extensions window doesn't open).	[12] [13]
Adblock Plus	Prior to 0.7.0.2	Having "Show tabs on Java and Flash" enabled may cause the ActiveX plugin (if installed) to ignore its configuration and run any ActiveX control, posing a security risk.	Update to version 0.7.0.2 or later	[14] [15]
	Prior to 0.7	Leaks memory	Update to version 0.7 or later	[16]
	All	Triggers a bug in Firefox 2.0 that causes some extensions and web sites to break, most prominently Google Notebook extension	Upgrade to Firefox 2.0.0.1	[17] [18]
All-In-One Gestures	All versions using Firefox 2?	May cause crashes. Also conflicts reported with spellchecker in Linux Mac OSX versions.		[19] [20]
All-In-One Sidebar	0.6.4 and prior	New extensions will not install. Also occurs in version 0.6.4 if updated from an earlier version or if used together with the SessionSaver extension.	Uninstall, then (re)install version 0.6.4. Disable opening the Extensions window in the sidebar (Misc. -> Extensions -> Open in Sidebar).	[21] [22]
Amazing Media Browser	0.17	The "Block all embedded objects" preference is set to "Yes" by default, causing embedded media normally handled by plugins to disappear, including Flash content. Also interferes with the IE Tab extension.	Change the "Block all embedded objects" preference setting to "No".	[23][24]
Bookmark Duplicate Detector	Prior to 0.3.0	Add Bookmark fails in Firefox	Update to version 0.3.0	[25]
Fasterfox	1.0.x	Hangs or slows down Firefox	Disable prefetching, select "Optimized" preset instead of "Turbo".	[26]
	All	Changes made by extension can interfere with Web site access, and persist after extension is uninstalled.	Reset defaults or create a new profile.	[27]
Filterset.G Updater	Prior to 0.3.0.2	Memory leak when used in conjunction with FlashGot	Update to version 0.3.0.2.	[28]
Firefox Google Toolbar	Prior to 0.2.1?	Interferes with spell checking in Firefox version 2.	Update to version 0.2.1. If that does not work, uninstall extension.	[29]
FlashBlock	All	NoScript blocks JavaScript, which is required by FlashBlock	Do not use both FlashBlock and NoScript together (NoScript includes Flash-blocking functionality)	[30]
FlashGot	Prior to 0.5.9.995	Memory leak when used in conjunction with Filterset.G Updater	Update to version 0.5.9.995.	[31]
ForecastFox	version 0.9.x and all satellite images versions?	Memory leak	Update or uninstall. There are unconfirmed reports that there are also memory problems with versions 0.9.3 and 0.9.4.	[32][33][34]
	All?	Causes excessive CPU usage with Firefox 2	Uninstall and install Forecastfox l10n	[35]
Google Browser Sync	All?	Causes excessive CPU usage with GIF animations	Uninstall	[36]
Google Toolbar (official)	1.0.* on windows 98, 2.0.20060404 beta and 2.0.20060515 beta	Causes a dialog to appear that says "A script on this page is causing mozilla to run slowly. If it continues to run, your computer may become unresponsive. Do you want to abort the script?"	The Google Toolbar is not compatible with Windows 95, 98, or ME. Fixed for supported OSs in latest version.	[37]
	2.0.20060404 beta and 2.0.20060515 beta	Leaks memory	Install the latest version from toolbar.google.com	[38]
	2.1.20060713	Causes excessive disk activity	Disable Google Safe Browsing or install the latest version from toolbar.google.com	[39]
Greasemonkey	All	Greasemonkey scripts do not work on sites blocked by NoScript	Set NoScript to allow JavaScript on sites you wish to use Greasemonkey scripts on.	[40]
	Prior to 0.6.3	Window title doesn't change when switching tabs	Update to a newer version	[41]
	Prior to 0.3.5	Major security flaw that could allow websites full access to your computer	Update to a newer version	[42]
Hebrew Calendar	Prior to 1.0.4.36	Causes "ReferenceError: JEvent is not defined"	Update to a newer version	[43]
IE Tab	All	Memory leak	Uninstall IE Tab and install IE View Lite	[44]
iMacros	Prior to 0.5.0.4	Causes 100% CPU usage	Update to a newer version	[45]
Linky	2.6	Gray bar below the status bar with red arrow.	Uninstall Linky.	[46]
McAfee SiteAdvisor	22	Firefox may fail to open after installing or updating the SiteAdvisor extension, which also may be installed as part of a McAfee software suite. This SiteAdvisor support article describes the problem as a conflict between SiteAdvisor and automatic proxy configuration scripts in Firefox.	Either follow the workaround in the SiteAdvisor support article or end the firefox process that remains in memory, start Firefox in Safe Mode and uninstall via Tools -> Extensions. If SiteAdvisor is a McAfee suite component it can also be removed using the McAfee uninstaller.	[47] [48]
	23	Firefox may crash with an error in Jar50.dll after installing or updating the SiteAdvisor extension or McAfee component.	Uninstall the SiteAdvisor extension or, if SiteAdvisor is installed as part of a McAfee software suite, remove the SiteAdvisor component using the McAfee uninstaller.	[49]
Mouseless Browsing	All?	Can cause excessive CPU usage	Uninstall Mouseless Browsing	[50]
Nightly Tester Tools	All	Allows incompatible extensions and themes to run; these incompatible add-ons can cause problems	Update your extensions and themes to those compatible with your version of Firefox	[51]
NoScript	All	Causes an illegal operation in the Windows Media Player plugin if it is blocking JavaScript on a page with embedded Windows Media	Do not block websites that have embedded Windows Media if you want to be able to play the media	[52] [53]
		FlashBlock requires JavaScript to work to block flash ads	Do not use both FlashBlock and NoScript together (NoScript includes Flash-blocking functionality)	[54]
		Greasemonkey scripts require JavaScript	Set NoScript to allow JavaScript on sites you wish to use Greasemonkey scripts on.	[55]
	All since 1.1.0	Java is blocked by default on untrusted sites	Uncheck "Forbid Java" in NoScript's Advanced options or, in version 1.1.3 and later you can temporarily allow Java content by clicking on its placeholder.	[56] [57]
	Prior to 1.1.3.9	Causes Firefox to hog memory	Update to 1.1.3.9 or later	[58]
"Numbered Links"	All	FormSpy (aka FireSpy) malware identifies itself as "Numbered Links". The real Numbered Links extension is harmless. See this forum topic for more information.	Uninstall the extension. Scan your system for viruses, particularly "FormSpy" and "Downloader-AXM".	[59][60]
ProCon	All	Replaces all words on webpages with asterisks (******) if set to "censure" words.	Uninstall ProCon, restart Firefox, reset ProCon preferences in about:config, restart Firefox, reinstall.	[61]
SessionSaver	All	Leaks memory	Uninstall SessionSaver and install Session Manager	[62]
	Version 0.2	Causes "unresponsive script" dialog when uploading files	Downgrade to version 0.2d	[63]
StumbleUpon	Prior to 1.9996	Changes Firefox's user-agent string and can make addons.mozilla.org think you have an older version of Firefox installed	Update to a newer version.	[64]
	Prior to 2.78	Causes excessive CPU usage	Update to a newer version.	[65]
SwitchProxy Tool	All	Causes new Firefox windows to freeze for a few seconds	Disable SwitchProxy's auto-update feature	[66]
Tabbrowser Extensions (TBE)	All	General slowdown, conflicts with other extensions, can cause Firefox to not work at all	Uninstall TBE, use Tab Mix or Tab Mix Plus instead	[67]
Tabbrowser Preferences (TBP)	All (for Firefox in some languages)	Puts a bar at the bottom of the screen which reads: <button id="catTabbedButton" label="&tabprefs.label;"	Uninstall TBP	[68]
	1.2.8.4	Puts a bar at the bottom of the screen which reads: %tabprefsDTD;	Uninstall TBP and install it directly from the author's website	[69] [70]
	Prior to 1.2.8.2	Pressing Ctrl+Enter in the address bar opens page in new tab instead of adding "www." and ".com" to the address	Update to a newer version	[71]
		Pressing home button opens homepage in new tab	Update to a newer version	[72]
Thumbs	Prior to 0.6.2	Leaks memory	Update to version 0.6.2 or later	[73]
User Agent Switcher	Prior to 0.6.4	Reinstallation or update causes hangs	Uninstall previous version in safe mode before installing new version	[74]
VeryDelicious	All	Software update screen on opening windows and downloading fiiles.	Uninstall VeryDelicious	[75]
Wizz RSS News Reader	2.0.0	Update causes Firefox to freeze	Uninstall previous version in safe mode then install the updated version.	[76]