I'm at a loss to explain this. I have a new (2-week-old) 14'' iBook with 1.5 GBs of RAM, and Firefox has somehow managed to eat up 1 GB of that in the past hour. I turned on Activity Monitor before I began. With all of my normal applications and Firefox open (nothing happening with any of them, just open) about 350 MB was being used. Then I started using Firefox, browsing through all the webpages that I would normally go through. I discovered that every time I closed an old tab and created a new one, the amount of RAM used would go up. If I closed and opened a new window, then RAM use would go up even further. Opening an image and then closing it caused RAM to go up. It was like every single action I did only caused Firefox to increase its RAM use. On top of that, I had to play an embedded Quicktime audio file in one page and the browser managed to eat up something like 90% of my CPU continuously for several minutes, beyond even the length of the file. I eventually managed to get myself up to about 1.37 GB of RAM used, and said screw it. When I finally quit Firefox, I checked Activity Monitor and found my RAM back down to about 400 MB used. What on earth is going on with this program?