Try the compatability reporter, it helps with some extensions. Firefox policy apparently is that although you have been using firefox 4 until now it should not be easy for you to go back to it as it is now unsupported, and so you should use Firefox 3,6 or 5. I can not openly directly post about going back to Firefox4 it is not official policy. I do agree with not using firefox 4, in most circumstances. I have Fx4 on my computer, but only for comparison purposes, however I feel some users are going to be desperate to go back if it worked with their extensions or websites and the other versions do not. See also * [/questions/839921#] * [[installing a previous version of firefox]] * https://addons.mozilla.org/en-US/firefox/addon/add-on-compatibility-reporter/ *http://kb.mozillazine.org/Go_back_to_an_old_version_of_Firefox If you are interested in the official policy and reasoning have a look at (but probably not a good idea to post in) the discussions: *[/forums/contributors/707043# No longer easy to download firefox 4] *[/forums/knowledge-base-articles/707029 {Proposed} Update to Firefox 5 ]