Type: http://about:config into Firefox's address bar
Then click the "I'll be careful, I promise!" button.
Right-click anywhere. Choose New>Boolean.
Make the name of your new config value extensions.checkCompatibility and set it to false.
Make another new boolean pair called extensions.checkUpdateSecurity and set the value to false.
Restart Firefox you're ready to rock uh surf.
Tested with Firefox Versions 3.x not tested with 4.x versions yet let me know how you get on with your comments.
