Your FireFox profile might have some corrupted data. Follow the instructions from this page:
Files that store information about the extensions you have installed can sometimes be corrupted. Deleting them can fix a number of extension issues; they will be regenerated, as needed, the next time you start Firefox.
Exit Firefox completely, then open your Firefox profile folder (read the linked article for its location) and delete or rename these files:
Starting in Firefox 4, also delete or rename:
- extensions.sqlite-journal (if found)
You may also need to delete or rename the compatibility.ini file, to rebuild some other files in the profile folder.
Note: Although the above files can be deleted, renaming them (e.g., "extensionsOLD.ini", "extensionsOLD.cache", etc.) is generally considered a safer option. This achieves the same result, but allows the user to retrieve any possibly required information from them later on.
You can find your profile folder using the instructions on this website:
Finding the profile folder
Using the Help menu - Firefox 3.6 and above
In Firefox 3.6 and above, you can open your profile folder directly from the Firefox Help menu, as follows:
- In the Firefox Button or menu bar, click "Help" and select "Troubleshooting Information". The about:support page will open. Under "Application Basics",
- On Windows and Linux, depending on Firefox version, click on "Show Folder" (Windows) "Open Directory" (Linux) or "Open Containing Folder".
- On Mac OS, click on "Show in Finder".
Note: The Firefox menu bar contains the File, Edit, View, History, Bookmarks, Tools, and Help menu items. On Windows, the menu bar may be hidden. You can press the "Alt" key to temporarily show a hidden menu bar.