Christian Legnitto, the release manager for Mozilla has confirmed that Beta 12 will be the last beta for Firefox v4.

I just wanted to send a quick note clarifying again that Firefox 4 beta 12 is the last planned beta. It may be confusing that nightly builds after beta 12 identify themselves as version 2.0b13pre. The versioning is merely a product of automation. This DOES NOT mean we are having a beta 13. For discussion on the proper value to change it to (if at all), see https://bugzilla.mozilla.org/show_bug.cgi?id=636190.

Published by Robert Rutherford