Hello, meleunig.

Install Add-on compatibility reporter extension-

https://addons.mozilla.org/en-US/firefox/addon/add-on-compatibility-reporter/

Now close and open Firefox 2 times. You are done.

Thanks for the assist although the Norton toolbar does still not come up on Firefox. Any other suggestions would appreciated.

Download Firefox 5.0.

http://releases.mozilla.org/pub/mozilla.org/firefox/releases/5.0/win32/en-US/

Uninstall Firefox 5.0.1 and install the version above (Firefox 5.0).

You do not need to take care that Firefox doesn't auto-update to Firefox 5.0.1. Firefox 5.0 on Windows and Linux will not update to Firefox 5.0.1, either manually or automatically. Firefox 5.0.1 was specially made to correct issues on Mac.

I don't know what will happen for Firefox 6.

Get in touch with Norton about this issue, they are incorrectly specifying the maxVersion in their Firefox add-on. They did that with Firefox 4.0, too - as soon as the 4.0.1 update was released by Mozilla, their extension was broken. They should be specifying "all 5 versions", not specifically 5.0 - that means "their stuff" only works in 5.0 and if Firefox releases a security update "their stuff" is broken and they have to update it.

You can get 5.0 from the Mozilla "Releases" server - http://releases.mozilla.org/pub/mozilla.org/firefox/releases/5.0/win32/en-US/ - no need to get it from a 3rd party.

@the-edmeister, They should be fixing it soon, Norton Internet Security 2012 will contain an updated toolbar (as always), so they might be fixing this issue too.