Comment 16 for bug 1020198

I think I have tracked the bug down to the "Global Menu Bar integration" extension, aka firefox-globalmenu. When I disable this, the menus work correctly.

Again, I never had this problem before Firefox 14.

firefox-globalmenu:
  Installed: 15.0.1+build1-0ubuntu0.12.04.1
  Candidate: 15.0.1+build1-0ubuntu0.12.04.1
  Version table:
 *** 15.0.1+build1-0ubuntu0.12.04.1 0
        500 http://us.archive.ubuntu.com/ubuntu/ precise-updates/main i386 Packages
        500 http://security.ubuntu.com/ubuntu/ precise-security/main i386 Packages
        100 /var/lib/dpkg/status
     11.0+build1-0ubuntu4 0
        500 http://us.archive.ubuntu.com/ubuntu/ precise/main i386 Packages
     7.0.1+build1+nobinonly-0ubuntu2 0
        500 http://archive.ubuntu.com/ubuntu/ oneiric/main i386 Packages