This memory leak is apparently already known, but I came across it for the first time last night. I was browsing some Classifieds threads on VWVortex and had loaded 2 threads with a large number of pictures in them. My entire system became extremely slow. In the Firefox tabs with the pictures, I could scroll the height of one image before the whole system had to take a break for 10 seconds.

I hit ctrl-alt-del to check for a run-away process to kill and discovered that Firefox was leaking huge amounts of memory...about 100Kb each second the 2 graphics intensive tabs for VWVortex were open. I closed all the other apps I had open at the time and browsed the threads as quickly as FF would let me and then killed FF, too.

It was quite astounding to see. Today, on this machine, FF memory usage is holding steady at 71,712MB. I should try to reproduce the behavior today, just for fun.