We mentioned earlier today about Firefox 3.5 RC3 Coming, it is now available for download. Whilst this may be as close to a final product, it is still a developmental version, therefore the usual disclaimer still applies:
Please note: Firefox 3.5 RC3 is a public preview release intended for developer testing and community feedback. It includes many new features as well as improvements to performance, web compatibility, and speed. We recommend that you read the release notes and known issues before installing this release.
Source: Mozilla Developers News