This morning Firefox was running just fine. Then I received the "New Updates" popup, listing updates to two extensions. I allowed it to download and install them, after which I was informed that the update wouldn't be complete until Firefox was re-started. But when I closed the browser I was unable to re-open it. The process runs, but the browser itself does not open. I rebooted the machine, but still got the same results.
I had something like this happen once before (several weeks ago) with Firefox, and I ended up having to uninstall it, rename a profile folder then re-install it, look up and RE-download and reinstall any extensions I wanted and reset all my preferences.
I don't want to go through all that again! Is there any way to avoid it? Any way to, perhaps, uninstall or disable the extension I think caused the problem (I believe it's the "stumbleupon" extension )...difficult to do when I cannot open the browser.
You don't mention what platform you're running, but you can try going into your profile directory, and in the "extensions" directory you will find a file called Extensions.rdf as well as a load of directories with random names. If you open the Extensions.rdf file in a text editor, you will see the references to the installed extensions with the directory name specified next to each. Then try removing the directory of the offending extension (renaming it should do), the attempt to restart Firefox.
(Do I need to say that you should really make a backup of your profile first before doing this kind of surgery?!)