CHeck out the web dude! It is a well accepted fact that Firefox 3 is a resource hog and trust me don't give me that crap of it consumes so and so amount of RAM on your system. I am a full time user of Firefox on Ubuntu; OS X & Vista. On all 3 platforms the amount of resources the browser consumes is outrageous and search google you will find a lot of people face the same.
PS: On OS X Firefox consumes 900MB to 1GB virtual memory with 3 tabs.
Here are some links on the web:
*www.pcmech.com/article/firefox-3-hogs-memory-like-crazy/
Here's your beloved Ubuntu:
*neosmart.net/blog/2008/firefox-3-is-still-a-memory-hog/
Here was another discussion on a forum where many have reported their insane RAM usages and some have normal usage:
*forums.whirlpool.net.au/forum-replies-archive.cfm/1003816.html
There are many links these, I went through a lot of blogs/sites/forums to find a solution to this problem, but in vain, that is the only reason why I will switch to Chrome once it get's a stable release on all platforms and will have extensions, till then I am bearing Firefox's antics.