LinuxPC.info

I had this problem on one machine. When closing firefox, and opening firefox again, a message appears about Firefox already running. A "killall firefox" will allow you to start firefox again. However the real problem is that Firefox sometimes hangs when closing it. When it does not, it often just crashes with a segmentation fault. You can fix this problem by removing a package called "gtk-qt-engine":

aptitude remove gtk-qt-engine