I’ve been testing the latest betas of Firefox for awhile now and Firefox 3 is shaping up to be very nice in my opinion. The biggest thing is the Mozilla team seem to have started plugging some of the memory leaks. Just my rudimentary test but after having both version open for two minutes and surfing the same few pages the memory usage of Firefox 18.104.22.168 is over 63 Mb and was still climbing when I stopped. While Firefox 3 the usage hovered around 55 Mb at the end and was steady. With some basic calculations thats over an 80% decrease (please don’t hold me to these numbers just very basic tests).
Some of the new features are very nice as well. My favorite being the adaptive autocomplete address bar. What this does is based on your usage patterns of the sites you visit the most and sites you visited recently and of course by letters your typing, it shows you the most relevant sites in the autocomplete menu. Also another nice thing is the ability to save your current tab layout when you quit. So when you come back to browsing everything is just how you left it.