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.

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

What problems are you having with Firefox 4?

Why do these idiots screw up something that was working? I use Yahoo.com as my home page. With 4.0 I can't even access it. There is not even an icon in 4.o for a home page.

And I hate that you can't "Go Back" to a list of pages - just the last one -that's it! Take it or leave it! And I can't sync my Nokia Ovi Suite either so I'm leaving it & reverting to V.3.