Mozilla introduced Beta 4 of Firefox 3 , with a boatload of stability fixes and a few improvements to the user interface. Mozilla says the beta -- like all the pre-release browser versions -- is for developers and testers only, but I've been using it as my primary browser since December and it works just fine.Get it here.

The What's New section of the release notes lists the major improvements in beta 4 (which was released today): "Firefox 3 Beta 4 includes more than 900 enhancements from the previous beta, including drastic improvements to performance and memory usage, as well as fixes for stability, platform enhancements and user interface improvements."

Specific improvements in this beta: Download manager, full-page zoom, Vista integration with Vista-specific icons and native user inteface widgets in the browser and Web forms, Mac integration to make the browser look more like a native OS X application, and integration with Linux.

Personalization improvements in this version include enhancements to the location bar and auto-complete:

Type in all or part of the title, tag, or address of a page to see a list of matches from your history and bookmarks; a new display makes it easier to scan through the matching results and find that page you're looking for. Results are returned according to their frecency (a combination of frequency and recency of visits to that page) ensuring that you're seeing the most relevant matches. An adaptive learning algorithm further tunes the results to your patterns!

Beta 4 also improves the speed of the JavaScript Engine, which in turn improves performance of applications like Google Mail and Zoho Office. And Beta 4 enhances memory usage.

I don't see much difference from Beta 3, but then again I've only been using it for five minutes. One minor problem: The FeedHub Feedback Extension, which worked in Beta 3, doesn't work in Beta 4. And Tab Mix Plus still doesn't work in FF4B4 -- it didn't work in previous betas, either.

We'll do a full-scale review if the new release looks sufficiently different from the previous betas. For previous reviews:

Review: Firefox 3 Beta 2 Continues Bookmarking, History Improvements

Review: Firefox 3 Beta 1 -- Packed With New Features And Rock Solid

I can't decide whether I love the word "frecency," or whether it makes me throw up in my mouth a little.