Firefox 4 was finally released for general use yesterday after much delay. I have been using the beta version and release candidates for quite a while and the biggest change for me was the UI. They have shifted to a minimal design like Chrome and Internet Explorer 9.
Firefox 4 has already been downloaded 4.5M times and counting. According to Computer World, it had already been downloaded over a million times in 3 hours!
Recently Chrome 10 and Internet Explorer 9 had also been released. Lifehacker as a nice article out comparing these different browsers so browser enthusiasts do check it out.