Firefox needs about 15-30 seconds to end and you can do nothing with the computer.
I read that Comodo 2.4 Version did have a problem with this phenomenon and you must set some extra rules for DLL's. After the new settings, FF was fast again.
I wonder what have those settings been since FF takes ages to terminate the process, CIS or Comodo or any other firewall doesn't matter at all... also it happens under Linux.
Last time I asked the FF developers they didn't care. So, to conclude - I pretty much doubt any CIS settings will fix anything there.