A third (and hopefully final!) Release Candidate of the Personas Plus add-on for Firefox 4 is available on the FTP servers. The RC works with Firefox 3+, current nightly builds, and Firefox 4 beta releases.
You can download the add-on here: https://ftp.mozilla.org/pub/mozilla.org/labs/personas/ — you want to get personas-1.6.2rc3.xpi.
If you find any issues (or if you test and everything seems OK), please post a comment here! Thanks!