The fourth beta of Mozilla’s upcoming Firefox 3 web browser is now out boasting no less than 900 fixes over the previous release, including improvements in the download manager, full page zoom, and significant improvements in speed and memory usage.

While beta 3 showed off some of the initial native user interfaces for specific operating systems, in beta 4 Mozilla has made some extra changes to offer better integration with Windows, Mac and Linux. But perhaps the most noticeable enhancement user-side is performance, with the company claiming a two-fold improvement when running script-heavy web applications compared to Firefox 2. You can read more about the new beta in the official release notes, or grab the beta itself for Windows, Mac OS X and Linux.