Firefox 3.1 Beta 2 also makes it easier to remove some parts of your browsing history and the TraceMonkey JavaScript engine is now on by default. Here's the full changelog:
This beta is now available in 54 languages - get your local version and let us know if it looks right. A new Private Browsing Mode that allows you to browse without Firefox storing any traces of where you’ve been - perfect for online holiday shopping! New functions that make it easy to remove the history of your past few hours of browsing, or remove all traces of a website. New support for web worker threads. The new TraceMonkey JavaScript engine is now on by default for web content. Improvements to the Gecko layout engine, including speculative parsing for faster content rendering. Removed the new tab-switching & preview behavior based on feedback from Beta 1 users Support for new web technologies such as the