You need to contact AVG about their plans for supporting Firefox 4. It is quite common for companies to only support a new version of a browser after it has been officially released, and not support it during the beta/release candidate phase.

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 - 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

There's no option on mozilla.com to download and install 3.6.16.

You can get 3.6.16 from http://www.mozilla.com/en-US/firefox/all-older.html

Thanks,Tony E.You made my day! What a relief to get my AVG Toolbar back on Firefox!

When I upgraded to Firefox 4 from 3.6.16, the HP SimplePass fingerprint reader on my laptop would not work with Firefox (it would not recognize web site login screens). Not knowing how this incompatibility could be fixed with Firefox 4, I saw my only alternative as going back to 3.6.16, a process I was concerned about doing. Thank you for your helpful advice and directing me to where I needed to go. I hope that by the time I need to upgrade to Firefox 4, this issue will be resolved by Mozilla.