I'm not sure why you think this is a bug. update-manager is only offering the xulrunner update, which is totally expected if you have it installed. In any case, it wouldn't have been a bug with xulrunner anyway.
** Changed in: xulrunner-1.9.2 (Ubuntu) Status: New => Invalid -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/742957 Title: FireFox 3.6.x with Xulrunner-1.9.2 update(s) offered when FireFox 4.0 is installed -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs