After updating to firefox-5.0-1.fc15.x86_64, I'm seeing a box glyph at the end of firefox's window manager title. xprop tells: WM_NAME(STRING) = "Bug List - Mozilla Firefox" _NET_WM_NAME(UTF8_STRING) = 0x42, 0x75, 0x67, 0x20, 0x4c, 0x69, 0x73, 0x74, 0x20, 0x2d, 0x20, 0x4d, 0x6f, 0x7a, 0x69, 0x6c, 0x6c, 0x61, 0x20, 0x46, 0x69, 0x72, 0x65, 0x66, 0x6f, 0x78, 0x7f Seems that there's a DEL char at the end of the string.
*** Bug 716512 has been marked as a duplicate of this bug. ***
This is going to be fixed with https://admin.fedoraproject.org/updates/firefox-5.0-2.fc15
This update has been pushed by caillon. Thanks for that.