To find out how much memory Firfox is using, press <Ctrl>-<Alt>-<Del> to launch Windows’ Task Manager, click the Processes tab, and scroll to the entry for firefox.exe. Depending on the size and number of pages you’ve viewed recently, the amount listed in the Memory (Vista) or MemUsage (XP) column can run into the hundreds of megabytes. To curb Firfox’s appetite, exit the program and then relaunch Firfox and Task Manager to see how much memory a fresh instance of the browser uses.

Full article at PC World