The results are pretty dramatic and fly in the face of Neosmart's findings. Note: I tried to keep the browsing as similar as possible for both browsers.
I then took both browsers for a good two hour browsing session, visiting some of the Internet's best 'hot sheets' websites and loading up 30 tabs for each browser (remember, IE7 and Firefox 3.0 are running in different virtual machines). The systems were given a meager 512Mb of RAM. I took two identical VMware virtual PCs, both running Windows Vista Ultimate SP1 32-bit. We haven’t seen it reach 1GiB+ like we have with previous versions, but it’s quite normal for Firefox 3 to be sucking up ~300MiB of memory right off the bat, with out a memory leak (the difference between memory leaks and normal memory abusage is that in a memory leak you’ll see the memory usage keep increasing the longer the browser is open/in-use). Firefox still uses a lot of memory – way too much memory for a web browser.
We’re sorry to have to break it to you, but if you thought it was too good to be true you were right. This morning I came across an article on Neosmart claiming that Firefox 3.0 is, despite the best attempts of the Mozilla dev team, still a massive memory hog.