Mozilla released Firefox 3.5 today. 3.5 delivers greater web standards compliance with support for HTML5 and CSS3. It's also much faster that Firefox 3. I would recommend all Firefox users download a copy.
Meanwhile a few weeks ago Apple released a new version of it's web browser, Safari 4. Recent benchmarking tests have shown that Safari is the fastest and most standards compliant browser out of all the big browsers (Internet Explorer, Firefox, Opera, Google Chrome). And yes even faster and more standards compliant that the just released Firefox 3.5.
Anyway both Firefox 3.5 and Safari 4 are available in Windows and Mac versions.