Firefox has no built-in option to launch at startup, you need to check the various methods that Windows uses to launch programs. For details see http://www.sevenforums.com/tutorials/1401-startup-programs-change.html

I checked all various methods provided in the posted link and still Firefox runs automatically at start-up. this issue happened after Firefox updated its self.

I had the same problem - but found the culprit...

I suggest you download the latest "Autoruns" tool

http://technet.microsoft.com/en-us/sysinternals/bb963902

Mine was started under the "logon" tab just uncheck the box next to firefox...

cheers Bob.C

I just got Win 7 and FF was acting like this. My solution was Start Menu - type MSCONFIG in the search bar and under the Startup tab in the System Configuration it lists all the programs that will start when the system boots. Uncheck FF and it won't start on boot up.