I reinstalled the browser. The bug still occures. Anyway I'm not gonna use Firefox any more because of the bug 783889:
https://bugs.launchpad.net/null/+bug/783889 -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/801432 Title: one of Firefox's files is in use by another application To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/firefox/+bug/801432/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
