Right click the Firefox icon, go to options, is "Open at login" checked?

Nope that is not checked either. :(

http://osxdaily.com/2011/08/25/disable-reopen-windows-when-logging-back-in-in-mac-os-x-lion-completely/

That still did not work. Firefox still auto starts when my mac reboots

You can try to uninstall (move to the trash) and reinstall Firefox to see if that helps.

It is also possible that another program tries to launch the default browser in case Firefox is set as such.

Would this have anything to do with it ? 6/20/13 1:43:08.972 PM WindowServer[89]: reenable_update_for_connection: UI updates were finally reenabled by application "Firefox" after 3.48 seconds (server forcibly re-enabled them after 1.00 seconds)

Closed the question in the other thread. We will track this answer here..