It's not quite official yet, as the Firefox 5 Beta is not ready for a release until May 17, but if you can't wait, you can already download the browser with the Firefox 5 label today. We have been playing with it for a few hours now and did not encounter any stability problems and even Mozilla says that it is now "safe to use" - other than the preceding Aurora release, which Mozilla claims is not for the faint of heart.
So, what is new? I'd love to tell you, but I am somewhat confused. There are some UI updates in the tab bar and a fine-tuned Panorama appearance. Mozilla says there is CSS3 support and I noticed that there is slightly better HTML5 support, according to HTML5test.com. In every day browsing, you won't notice the difference and it is somewhat disappointing that Mozilla may miss the integration of the Home Tab as well as Tab Apps. The bottom line: there is not much to talk about.
There is still some time until the Beta is released. However, at this time, it is basically a patch for Firefox 4 and Mozilla may have a tough time justifying the version upgrade. The company still complains that not enough people are using the developer channels - apparently there are not quite 100,000 users who have signed up so far. Mozilla wants at least 1 to 4 million developer/beta testers for its Firefox browser.