Setting the StartupWMClass value to Shredder in the thunderbird.desktop file, solved the problem for me.
-- StartupWMClass value in thunderbird.desktop file is not correct https://bugs.launchpad.net/bugs/600217 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
