Dumped Firefox, even after the tweaks I made a few days ago. I suspect it was having trouble with the number of tabs I had open, but after a certain point (maybe 8 or so) it just bogged way down and all my limited memory (a throbbing 640 Mb) was gone. Closing FireFox would free up a couple hundred meg. With Safari 3 open, I have 90 Mb free. I suppose a couple of tabs will start to eat into that (but how much should a tab weigh, if you like?).
And yes, I could buy more memory, since others have been successful adding a 1 Gb stick in place of the 512 Mb. But I would rather buy a new MacBook. If I could justify it against any income at all, I’d get one in a heartbeat.