the last "old" version is 3.6.16 and is available here: http://www.mozilla.com/en-US/firefox/all-older.html

Do not delete your bookmarks and they can be automatically transferred.

I am running Win 7 Pro, Firefox 4.0.

I had to disable Extensions: Flashblock and WOT as they were up to date but still not compatible with FF ver 4.0

Did you try starting Firefox in safe mode; this disables the add-ons?

Also I would recommend that you try downloading Firefox 4 again and save it to a new location in case your first download is corrupt.

After downloading, disconnect from internet. Scan the download with your security software and then turn off ALL other programs including security software, choose restart the software after reboot if your security software has such setting. Install the Firefox 4.0 and then reboot your computer. Make sure all security software is up and running, reconnect to internet and test Firefox.

Firefox SafeMode? - A troubleshooting mode.

1.You can open the Firefox 4.0 SafeMode by holding the Shft key when you use the Firefox desktop or Start menu shortcut.

To exit the Firefox Safe Mode, just close Firefox and wait a few seconds before using the Firefox shortcut to open it again.

For more help, see this: http://support.mozilla.com/en-US/kb/troubleshooting+extensions+and+themes

I contacted Norton and they say I am still protected while in the internet, I just do not have the functionality of the Norton Tool Bar. There will be an update for Firefox 4 available in May.

Glad they at least told you that there would be a release in May. They could not tell me much the other day.

May still seems like a long way off, especially when they knew that the new release was coming out.

Except for Norton's Tool Bar, Norton Internet Security 2011 works fine with Firefox 4. It always takes Norton awhile to update their software to have their Tool Bar work with Firefox Major Releases.

In addition to the Norton toolbar issue, Firefox 4 has disabled my Google Search memory function; while I can individually type into Google Search any term, its memory association feature is inoperable; e.g., if I type "Google", then in the memory listing below "Google toolbar Firefox 4" appears but it cannot be activated into Search; therefore I have to retype the whole terms into Search.

Google Search auto fill still does not work in Firefox 4; I replaced Firefox 4 with Firefox 3.6.16 and Google Search auto fill works fine. When/ how is this fault with Firefox 4 going to be corrected?

Norton has fix. See: http://community.norton.com/t5/Norton-Internet-Security-Norton/Norton-Toolbar-5-5-incompatible-with-Firefox-4-RC1/td-p/411556/page/2

I downloaded this Norton hotfix, and it solved the problem.

http://community.norton.com/t5/Norton-Internet-Security-Norton/Firefox-4-compatibility-hotfix-is-now-available/td-p/428894

While Norton's "fix" corrected their toolbar problem in Firefox 4, I still have the Google Search problem of its memory list remaining inoperative in Firefox 4 .

Long conversation with Norton. You are NOT protected online! They are working on an update, and hope to have it sometime in MAy 2011.

Norton told me that I was protected online. What new information do you have?