Today I had a funny thing happening with Firefox. Some Add-ons (Extensions) appeared to be not working, but the one which I use via a keyboard shortcut did work. The Add-ons dialog (via Tools/Add-Ons) also didn't work, all the screens didn't show the installed add-ons nor did it show the add-ons site.
The solution is described at the Mozilla support forum, but not very clearly, so here's the minimum amount of steps:
- On the menu bar, click on the Help menu and select Troubleshooting Information. The Troubleshooting Information tab will open.
- Under the Application Basics section, click on Show in Finder (on Windows it might be called Explorer, I don't know, don't use it anymore). A window with your profile folder will open.
- Go back to Firefox and quit it completely
- Go to the folder window opened in step 2
- Delete all files with the name extensions (extensions.rdf, extensions.cache, extensions.ini, extensions.sqlite) and compatibility.ini in the Firefox profile folder. Do NOT delete the folder called extensions!
- Start Firefox again. All add-ons will now behave as being newly installed, so Firefox might have to restart itself again)