I solved this one today on a Mac. The problem appeared when I was copying the profile from one user A to another user B on the same machine. In that profile folder were three files and one subfolder named 'extensions'-something that seems to contain a folder for any extension user A installed. After the following procedure I had to reinstall all extensions, but mirically all setting were there. In (for) any case remember to have a backup of your data. Here is what I did: Stop Firefox; rename Profile to Profile-old; Start Firefox; Stop Firefox - now you got a new clean Profile folder - copy the extension folder and the three extension files from the new Profile to Profile-old; delete Profile; rename Profile-old to Profile; start Firefox; reinstall extension; done Cheers, Cabiman