Credit Tony E Firefox is highly customizable and you may be able to customize it to meet your needs. If you do not like the new UI, you can make Firefox 4 look and behave more like Firefox 3.6, for details see http://www.computertechtips.net/64/make-firefox-4-look-like-ff-3-6 To downgrade to Firefox 3.6 first 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. See https://support.mozilla.com/kb/Uninstalling+Firefox You can then install the latest version of 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

I also had a huge problem after downloading Firefox 4. After re-installing Firefox 3.6 like proposed all problems are solved. Thanks!