Try: *http://kb.mozillazine.org/Preferences_not_saved ---- You can also try to delete the files extensions.* (extensions.sqlite, extensions.ini, extensions.cache, extensions.rdf) and compatibility.ini in the Firefox [[Profiles|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, not compatible, extensions in "Tools > Add-ons > Extensions" then click the Tools button at the left side of the Search Bar (or click the "Find Updates" button in older Firefox versions) to do a compatibility check or see if there is an update.