Norton wasn't prepared for the release of Firefox 4.0 (they never are prepared, it seems).
The extensions API for Firefox 4.0 was locked down over 5 months ago so that security vendors could start working on updating their products for the release of Firefox 4.0. Symantec / Norton pulls this crap of waiting until the last minute for every Firefox major release (like they're surprised by the release of a new version), inconveniencing their paying customers by making them wait a month or two while they get their shet together.

A Norton 360 user has reported that the eta for an update is sometime in May. Those Norton clowns just can't see their way clear to just support the browsers that their users want to use, they always want to roll the update for Firefox into a new release of theirs and charge you for the new version. (They claim they are extending your existing agreement, but from some of the reports I have read, they don't really do that.)

If you want to revert to 3.6.16 see this.
http://support.mozilla.com/en-US/kb/Installing+a+previous+version+of+Firefox

3.6.16 is available here.
http://www.mozilla.com/en-US/firefox/all-older.html

Thanks for your reply, i will keep firefox 4 installed. i will use my internet explorer until i get a new antivirus in a few days.

I went ahead and reverted back to firefox 3.6.16. version, thanks for your help on 3-25-2011.