Only two weeks after the release of Firefox 3.0.12, the Mozilla Project has issued another release of Firefox 3. Firefox 3.0.13 includes several security fixes.
Rather than updating to this release, I recommend updating to the latest version of Firefox 3.5. Firefox 3.5 includes several performance updates that make it much faster than Firefox 3. Additionally, Firefox 3.5 includes useful features such as Private Browsing and the improved location bar.