The problem with the iPlayer was not just how to kill Firefox but more far-reaching.  Using youTube I finally got around to somewhat understand what was happening:
When using the Lirc-mouse to activate a control of the embedded Adobe Flash player (such as the pause/play button) it seemed as if the Firefox was loosing focus.  It would not accept any keyboard shortcuts by way of the Lirc remote or by way of the keyboard.  This applieed to the exit shortcuts Ctrl-q and Ctrl-Shift-w.  Only Alt-F4 worked to kill Firefox using the keyboard, but not as a remote command.  The only commands that could be executed were the pulseaudio volume commands.  Sending further keyboard commands it seemed lock up even more also sopping the volume commands and sometimes even causing the irexec deamon to be killed.
Could not find how to get the focus back, and it thus seems as the workaround is to watch the video and then exit at the top corners using the lirc mouse and if needed restart the application.  Any suggestions?