From the 'good things come to those who wait' files:

At long last, Mozilla today is releasing Firefox 3.1 Beta 3. The Beta 2 release was out out in early December, itself a month overdue.

So what's in the new Beta 3? 

Mozilla has improved the Private Browsing Mode (aka Porn Mode) to make it even more private. The general idea behind Private Browsing is to have a browser session where the cookies and history file are not saved beyond the actual session. 

On the speed front, the TraceMonkey JavaScript engine gets stability and performance improvements. TraceMonkey in my view is a critically important feature, perhaps the most important new feature in Firefox 3.1 as a whole. The general idea is that it is faster than the JavaScript engine in Firefox 3.x and is competitive with Apple Safari's  Nitro JavaScript and Google Chrome's V8 JavaScript engines. Faster JavaScript engines means faster code execution means faster web experiences.

Mozilla also claims to have made improvements to the core Gecko rendering engine that will make content rendering faster overall. It's great to have fast JavaScript, but a faster Gecko in combination is really key.

Though this is Beta 3 for Firefox 3.1, it's actually the last Firefox 3.1 release period. The next beta is going to be called Firefox 3.5 Beta 4 in order to give the release more stature with the bigger release number. Firefox 3.5 Beta 4 and is currently targeted for an April 14th release.