What add-ons are you having problems with? There may be updates to the add-ons that are not being picked up, sometimes the add-on developer has made a version for Firefox 4 but not made it available on the add-ons site. There may also be alternative add-ons with similar functionality. It is also possible that an add-on you are using has been discontinued. ------ To downgrade to Firefox 3.6.* you can uninstall Firefox 4, but do not select the option to "Remove my Firefox personal data". If you select that option it will delete your bookmarks, passwords and other user data. You can then install Firefox 3.6.* available from http://www.mozilla.com/en-US/firefox/all-older.html - it will automatically use your current bookmarks, passwords etc. To avoid possible problems with downgrading, I recommend going to your profile folder and deleting the following files if they exist - extensions.cache, extensions.rdf, extensions.ini, extensions.sqlite and localstore.rdf. Deleting these files will force Firefox to rebuild the list of installed extensions, checking their compatibility, and reset toolbar customizations. For details of how to find your profile folder see https://support.mozilla.com/kb/Profiles