'''Good to know you solved your own problem by simply installing another extension''', I like solutions that aren't going to cause extra work, or loss of data. Here is what people normally have to do for missing extensions, as if not installed.-- <br>https://support.mozilla.com/questions/826729 :http://kb.mozillazine.org/Unable_to_install_themes_or_extensions_%28Firefox%29 FWIW, renaming or deleting extensions.sqlite and the other files beginning with "extensions." causes the files to be rebuilt from the extensions directory, so nothing is lost, but they will be restored in alphabetical order. I've solved places.sqlite problems by simply restoring a bookmarks backup, or creating a bookmarks backup and restoring that rather than face loss of history. Please mark as solved so others will see your answer when looking for solved problems as solutions to there own or other people's problems.