Awesome Bar
One obvious change is the Smart Location Bar, also known as the 'Awesome Bar'. As you type in a URL, the Awesome Bar searches through your history and bookmarks and presents a drop-down list of recently accessed pages with that same keyword. It works even if you already know the URL. Some people have found it annoying, so there is a way to disable it requiring a small tweak to the about:config file. An Add-On further allows you to learn which of the search results you want to always be on top.
6%
3%
"Firefox 3 offers faster rendering, a vastly reduced use of system resources and clever new data-mining tools for your bookmarks and browser history."
And, a new code execution vulnerability right from day one. It say a lot for the browser that so many hoped would live up to a brief reputation riding on how secure the browser was supposed to be. Then again, if you release software and claim that hackers can't break it then you are asking for trouble and it looks like the chook has come home to roost.
I'll stick with IE - better the devil you know, and it means one less application to worry about.