I had the same problem after a system restore. After looking around I noticed a window open with the title "Mozilla Firefox (Safe Mode)". Even though my computer wasn't in safe mode, it's only Firefox's safe mode.

The window contains 5 or 6 check boxes like "reset preferences" or "reset tool bars", I selected all the boxes except the "reset bookmarks".

As soon as you select the one's you want you click the "Restart" button in the bottom corner of the window. This only restarts Firefox, not you computer. I just hit restart and a new Firefox session popped right up and I haven't had a problem since.

It is always better to do a reinstall of Firefox after doing a system restore. The result of a system restore can be unpredictable and may cause some files to get replaced by older versions. That can also happen with files in the Firefox Profile Folder. Files with the file extension .ini and .js are the most obvious candidates.

Delete sessionstore.js and sessionstore.bak in the Profile Folder
If you see files sessionstore-##.js with a number in the left part of the name like sessionstore-1.js then delete those as well.

See http://kb.mozillazine.org/Session_Restore

See also:

• Troubleshoot Firefox crashes (closing or quitting unexpectedly)
• Troubleshoot and diagnose Firefox problems