I can get it up to 2GB virtual memory in a morning's average browsing.
Virtual memory has no real bearing on the quantity of physical ram occupied by an application. Virtual memory is a large, expandable, virtually contiguous slice of memory provided by your OS's memory manager. What you're looking for is resident memory. My current FF3.5 session is 'using' 973 MB virtual memory but in reality only 163 MB physical (resident).
Any sufficiently advanced bug is indistinguishable from a feature. -- Rich Kulawiec