See:

• http://kb.mozillazine.org/Lost_bookmarks
• http://kb.mozillazine.org/Locked_or_damaged_places.sqlite

You can delete the files extensions.* (extensions.rdf, extensions.cache, extensions.ini, extensions.sqlite) and compatibility.ini in the Firefox profile folder to reset the extensions registry. New files will be created when required.

See "Corrupt extension files": http://kb.mozillazine.org/Unable_to_install_themes_or_extensions

If you see disabled extensions that are not compatible on the next start in "Tools > Add-ons > Extensions" then click the "Find Updates" button to do a compatibility check.

You may also need to "Reset all user preferences to Firefox defaults" on the Safe mode start window.

well, since firefox chose again, as always to release an update that is bare naked i.e. most extensions are not compatible now, it becomes tiresome, with every 4th or so update to have to reset etc. - just because FF does their testing at the expense/time of the user. It should not be the user that has to scramble for solutions - but then again what else is new, we are used to it from microsoft crappy releases, that leaves millions high and dry - sad to say, that Firefox joined those ranks, rather than stabilizing what was once the best browser there was - it is no longer the case.