Firefox users are be automatically prompted to install a new release of Version 3 of Firefox. But Version 4 of Firefox was released two days ago, and makes a lot more sense as an upgrade, assuming you don't mind a bit of a change in visual appearance, and operation.
Wikipedia already has a Firefox 4 entry:
http://en.wikipedia.org/wiki/Firefox_4
I've read elsewhere that Firefox 4 borrows heavily from Chrome. Never having seen Chrome, I don't know.