Have you tried starting in Firefox's Use Troubleshoot Mode in Firefox? Hold the shift key when double-clicking the Firefox program icon. In the Safe Mode dialog, do not check any boxes, just click "Continue in Safe Mode."

If Firefox runs in Safe Mode, there may be a problem with one or more of your add-ons or custom settings. If you restart in Safe Mode, you can disable all your add-ons using a checkbox and see whether that helps.

Before taking that step of disabling anything, I recommend backing up your Firefox settings in case something is inadvertently deleted. See Backing up your information. (You can copy your entire Firefox profile folder somewhere outside of the Mozilla folder.)

Does it make any difference?

Create a new profile as a test to check if your current profile is causing the problems.

See "Basic Troubleshooting: Make a new profile":

• https://support.mozilla.org/kb/Basic+Troubleshooting#w_8-make-a-new-profile

If the new profile works then you can transfer some files from the old profile to that new profile, but be careful not to copy corrupted files.

See:

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox