Firefox won't start but when I open a link that opens Firefox it works fine?

This article describes what to do if the Firefox window doesn't open when you click the Firefox icon. If you get a message you can dismiss (e.g. Classes'@ ... ;1' is undefined", "onload error TypeError: ...", "Exc in ev handl: ...") and can open Firefox, see Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems. If Firefox starts but won't load any websites, see Websites don't load - troubleshoot and fix error messages.

If you get the "Mozilla Crash Reporter" window when you start Firefox, see Firefox crashes - Troubleshoot, prevent and get help fixing crashes for solutions. See "Firefox is already running but is not responding" error message - How to fix it for solutions. If you see the message, "XULRunner - Error: Platform version is not compatible with minVersion " depends on version number), after a software update, use another browser to download the Firefox installer from mozilla.org/firefox, save it to the desktop or other location, delete the Firefox installation directory and then reinstall Firefoxreinstall Firefoxreinstall Firefox.

If Firefox still does not start, see the Firefox will not start after updating section below. If you get another error message (e.g. "XML Parsing Error: undefined entity Location", "Secure Connection Failed ... uses an invalid security certificate"), see Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems. If you click the Firefox icon but no Firefox window opens and no error message is shown, a simple first step is to restart your computer and then try again.

If Firefox still does not start, see the following sections. If Firefox fails to start after an update, first check the Hot Topics section to see if it contains a solution. If you use certain versions of ZoneAlarm or other Internet security software that includes a "Virtual Browsing" feature, it can prevent Firefox from starting.

Check virtualization settings and clear the virtual cache, if your Internet security software includes this feature, or visit the software provider's support site for more help. If Firefox previously worked but stopped after you installed extensions or themes, see Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems. If Firefox previously worked but suddenly doesn't start, it may be due to some corrupt data in your settings.

Uninstalling and reinstalling Firefox would not fix this problem because your settings are not removed on uninstall. To test to see if this is the problem, use the Profile Manager to create a new profile. If the problem goes away, you can then move your bookmarks and other important settings into the new profile.