FWIW, I have had no end of trouble getting Firefox to run on my new system. Starts off fine after a clean install/restore but after some time it always crashed and would not load again, and always gave me the same set of error messages - all related to Extensions or Add-Ons, of which I only had 2 I'd put on myself and trusted from XP. Googled my heart out and never found a solution, nor saw anyone else who had encountered this total loss of Firefox. Lots of posts referring to crashes but none about a total Firefox blackout. NOTHING, and I do mean nothing, would fix the problem. I tried all this: run Firefox Safe Mode; removing all addons and cleaned up all the extension entries; Uninstalling and Reinstalling; cleaning profiles; removing all Mozilla folders; deleting all registry entries. i.e. What you'd think would have removed any trace of Firefox on my computer. Because I refuse to use Explorer and don't like Opera that much, I would restore my clean backup and go again, only for the crash to reoccur
Finally, after cleaning the registry etc. etc. I tried installing to a new folder (Firefox instead of Mozilla) and so far so good. Why this works I have NO idea. Wish I'd know how simple that was in the first place - HTH someone else somewhere along the line.