worse than it should be

I wonder why other processes have to suffer so much at all for Firefox's memory allocation? It ought to be possible (*) to limit the rate at which a process can cause pages belonging to other processes to be swapped out, and to ensure that the other processes never go below a certain threshold of physical pages (possibly a lower threshold for processes that are rarely used, but even they are probably in memory in the first place for a reason).

(*) Yes, I know someone still has to do it. If no one else does, and I don't get told at once on LWN why this is such a bad idea, perhaps I will have a look at if I ever have a free minute...