Mozilla Firefox 3 Beta 4 is now out boasting no less than 900 fixes over the Beta 3 release.

On the surface Mozilla has again made some minor cosmetic changes to Firefox 3 that vary depending on whether you're running Windows XP, Windows Vista, Linux/GNOME or MAC OS X.

The 900 fixes though seem to be mostly in the bug fix and performance improvement area according to Mozilla's release notes:

[Improved in Beta 4!] 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. Many of these improvements were based on community feedback from the previous beta.

While 900 enhancement sure sounds like alot it's actually a drop from the Beta 3 release when Mozilla boasted 1300 improvements - though in that release they claimed  that only 50 or so were specifically memory related improvements.

I suspect that as was the case with Beta 3 alot of the memory improvements in Beta 4 come by way of the XPCOM (Cross Platform Component Object Mode) cycle collector that identifies objects that aren't being used and releases them from memory. XPCOM was first deployed as part of the Firefox 3 Beta 1 release in November.

Mozilla has planned for at least one more Beta (Beta 5) before Firefox 3 will hit the release candidate stage. It's not yet clear how many release candidate there might be or how long it will actually be till Firefox 3 is considered to be final. From my point of view, it's not a race at this point. IE 8 is just in Beta 1 (and it's got a tonne of issues), it's far better for Mozilla to fully shake and bake Firefox 3 before releasing it to the masses. After all who wants a buggy browser?