Do you have a Google account or use iGoogle? My Firefox 5.0 started doing this add-on manager tab thing after a reinstall. I went manually to google.com (typed the address in the URL bar), signed out of my google account, and then changed that generic Google page to my home page in Firefox options. Then I signed back in to my Google account, navigated back to iGoogle, and then made that my home page again in Firefox options. No more Add-On Manager tabs when I click on the home button! I know that process was a little complicated sounding. If you didn't follow that, I'd suggest just changing your home page a couple of times, logging in and out of Google if you have an account, etc., until it goes away. Worked for me. :-) Good luck. It annoyed me so much, I was about to switch back to IE. [shudder]