The release notes of the new browser note that version 5 includes more than 750 changes from Beta 4, which was released not even a month ago.
New features and changes in this release include improvements to the user interface based on user feedback, including changes to the look and feel on Windows Vista, Windows XP, Mac OS X and Linux.
Mozilla has also made changes and fixes for new features such as the location bar autocomplete, bookmark backup and restore, full page zoom, and others. Developers have also worked to improve security, web compatabilty and stability.
You can find out more about all of these features in the "What?s New" section of the release notes.
Testers can download Firefox 3 Beta 5 builds for Windows, Mac OS X and Linux in 45 different languages.