Most problems with Firefox can be fixed by following the troubleshooting methods described below. Try these steps in order. If one doesn't work, move on to the next one. If you need extra help with any of this, we have a community of volunteers standing by.
Sometimes problems can be fixed by simply restarting your computer and then starting Firefox again.
Many problems with loading web pages can be resolved by clearing Firefox's cookies and cache:
Firefox Safe Mode is a troubleshooting mode that disables all extensions, uses the default theme, turns off hardware acceleration, and uses default toolbar settings and controls, among other things. To start Firefox in Safe Mode:
Some Firefox issues can be caused by a problem with one of the Firefox program files. Follow these steps to completely remove and reinstall Firefox. This process will not remove your Firefox profile data (such as bookmarks and passwords), since that information is stored in a different location.
Now start Firefox and check to see if your problem has been fixed. If it hasn't, continue with the next troubleshooting method.
The Refresh Firefox feature can fix many issues by restoring your Firefox profile to its default state while saving your essential information.
Sometimes files in your Firefox profile folder that correspond to the essential information that a Firefox Refresh doesn't remove (such as bookmarks and browsing history) may be causing the issue. You can create a new, additional profile which will not contain any of your old Firefox data. See Use the Profile Manager to create and remove Firefox profiles for instructions.
If you've tried all of these troubleshooting methods and you're still having problems, the issue may be with other software or hardware on your computer.
For more information on any of these solutions, please check the related documentation.
Click the menu button and choose Add-ons. The Add-ons Manager tab will open.
If your problem goes away when your plugins are disabled, see the Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems article to learn how to narrow down the cause.
Some Internet security software (including antivirus, antispyware, and firewall programs) can cause problems with Firefox including blocking it from opening websites, crashes, and more. Often you can open the program's settings, remove Firefox from its list of allowed or trusted programs and it will be re-detected and things should start working again. If your program is listed at the Configure firewalls so that Firefox can access the Internet article, you can get specific instructions for how to properly reconfigure it.
Malware (short for "malicious software") can cause problems with Firefox. Periodically, you should scan your system for viruses, spyware, or other malware. For more information, see Troubleshoot Firefox issues caused by malware.
Based on information from Standard diagnostic - Firefox (mozillaZine KB)