Mozilla released Firefox 4 Beta 9 and is available for download through its FTP servers, you can able to read official announcement on Mozilla blog and also will be available as download from Firefox beta page later, currently beta version being distributed to mirrors.
Firefox 4 final will be available in February according to Mozilla, but this release is more of polish to prior released Firefox 4 Beta 8 version and bug fix release. We can expect another beta and then may be release candidate next to follow.