Symantec need to update their Firefox add-ons so that they are compatible with Firefox 4. They have indicated that for Norton 360 they plan to release an update to Norton 360 to support Firefox 4 in early May - http://us.norton.com/support/kb/web_view.jsp?wv_type=public_web&docurl=20100720113635EN&ln=en_US

I do not know about the time scale for updates for other Norton products. Pending the update by Symantec, if you want to use the Norton add-ons you will need to downgrade to Firefox 3.6.

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

Thanks so much for the info, it was a huge help!!! I was going to uninstall 4, and reinstall 3.6 but I'm relatively new to this kind of thing and didn't want to screw anything up!! I don't want to remove things I know nothing about, like a profile folder!! Maybe my best bet would be to wait till Norton catches up!! Again, my thanks for your help. It's nice to talk to someone who knows a thing or 2 about this stuff!!

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

Better to wait until Symantec issues the fix in May. I HATE having to go to IE8 to use my ID Safe with Firefox up and running another window because they were not on top of the release of FF 4.0. That may have been because the Mozilla folks didn't give them an advance beta to diddle aforehand...Geeks have communications issues just like us normal people!!! That's the fix until they do, by the way, in case you really aren't paying attention.

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

A Norton support forum admin posted that on 4/07/2011 - 10 days ago.

I had the same problems, when i installed firefox. I didn't see Norton, so I uninstalled firefox. So what did you finally do about the problem? I am currently using Internet Explorer, and it is very slow and I cannot do certain things on Facebook. So I'm waiting for some kind of resolution.

I have received many helpful hints, but not being too tech savvy about installing, uninstalling and fixes, I too use Internet Explorer because Norton is there. I'll wait till my Norton subscription is up, and hopefully the new Norton will be compatible with Firefox, because I do prefer using Firefox and have been using it for a couple years.