the SIGSTP could be an answer, if it could
be sent to firefox and the plugin compartments
on a user switch…

The kill is too strong since it looses the context
of the pages which are active.

It would resolve a major problem that I have at
home but also in my university lab where we also
have user switching activated — with machines getting bogged down by background sessions

I am often confronted with the following problem-

I have carefully set up user switching on my macs-
so my kids can play web games, mess about on youtube, without impacting my own work environment.

There are thus often two or three instances of
firefox active. However, even when a person
is not using a session firefox can
actively eat lots of CPU, and set of the fans,
generally slowing the whole system down.

Is there a way of setting up a much stronger throttling of firefox if it is not in the active
session… There was already some talk about this a couple of weeks back for tabs, but this seems even more
useful. Even music playing, (for instance), in one of
these sessions is not sent to a speaker