Firefox 3.5 Beta 4 went into code-freeze on Wednesday and just went through the QA build process this evening. If it passes initial testing, this release will become the official Beta 4 release. At the time of this post, Firefox 3.5 still has 68 release-blocking bugs, including one that could affect the international-language Beta 4 releases.
You can download the build here (Edit: how come we can't enter ftp:// URLs in a link?), or just wait a week or so until it is posted through the official release channels.
Check out the weekly status meetings, which give good info, here.