have you been able to reproduce the bug?
what happens if you run killall firefox in a terminal to force exit?
** Changed in: ubuntu
Status: New = Incomplete
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Kill Application button leaves message box on screen forever.
https://bugs.launchpad.net/bugs/211150
You received this bug
*** This bug is a duplicate of bug 59143 ***
https://bugs.launchpad.net/bugs/59143
** This bug has been marked a duplicate of bug 59143
Force quit applet doesn't remove modal window when pressing ESC
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Kill Application button leaves message box on screen forever.
