I was right about the driver thing. I've installed 173 again and Firefox is behaving normally again, so probably it was not a Firefox-bug after all.
I'm marking it as Invalid. ** Changed in: firefox (Ubuntu) Status: New => Invalid -- firefox goes "full screen" at startup or when clicked on a link outside firefox https://bugs.launchpad.net/bugs/262388 You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs