The StartupWMClass key in the mozilla-thunderbird.desktop file is incorrect in Fedora 17. It should be set to just "Thunderbird", not "Thunderbird-bin". This prevents the thunderbird icon from showing up twice in certain docking applications. The StartupWMClass value was found by running "xprop | grep WM_CLASS" and clicking a Thunderbird window. This is exactly the same as bug 844860, except that this bug report is for Thunderbird.
Added to rawhide.