The Beta released which is available in their Mozilla Download page (available in different languages) is not intended to common or nontechie users. This is designed for testing purposes only, its target are those web developers and their Mozilla testing community.
"Firefox 3 is based on the Gecko 1.9 Web rendering platform, which has been under development for the past 31 months. Building on the previous release, Gecko 1.9 has more than 12,000 updates including some major re-architecting to provide improved performance, stability, rendering correctness, and code simplification and sustainability" based on their Mozilla Firefox 3 Beta 4 release notes.
"[Improved in Beta 4!] Firefox 3 Beta 4 includes more than 900 enhancements from the previous beta, including drastic improvements to performance and memory usage, as well as fixes for stability, platform enhancements and user interface improvements. Many of these improvements were based on community feedback from the previous beta."