On the same day that Apple released the public version of Safari 4 for Windows and Mac, Mozilla published an update to its Firefox 3.5 beta. Available for Windows, Mac, and Linux, they're not calling this a beta version, but it's not a release candidate, either.

Within the next 24 hours, the Firefox 3.5 beta 4 will auto-update to what Mozilla is calling a "preview" version. Users can also force the update by going to the Help menu, then Check for Updates. At the time of writing, it doesn't appear that users can download the 3.5 Preview version directly.

In a press release, Mozilla said that Firefox 3.5 Preview will leverage the more than 800,000 users of the 3.5 beta to further test changes made to the browser, indicating that it feels the browser is fine for daily use but might still contain significant problems.

The update makes a large number of bug-fixes for stability, tweaks the Mozilla JavaScript engine TraceMonkey, and improves support for the baked-in Ogg-based open audio and video standards. Overall, it sounds like this should be called beta 5, although the "preview" moniker will likely get good buzz and Microsoft proved with the Windows 7 beta that utilizing your fan base to find potential problems isn't necessarily a bad thing.

Firefox's slight change to the tab buttons: gray instead of green. (Credit: Screenshot by Seth Rosenblatt/CNET)

I also noticed that there's a minor interface change in the Preview. Tab management buttons are now gray on gray, changed from the green on gray.

Mozilla's open-source evangelist, Christopher Blizzard, is also highlighting the new developer features coming in Firefox 3.5 in a new blog.

The Firefox milestone announcement can be read here.