I'm sitting in the Mozilla BoF at LISA'11 and they just now announced that beginning with Mozilla 10 (currently in the Aurora status, which is similar to Alpha), not only will plugins become compatible by default, but that upon release, it will be the first "Extended Support Release".

The support term that Mozilla will offer will be"about one year". No new features will be backported from later revisions, but security updates will be added.

By default, Mozilla will still prompt users to upgrade to newer available releases, but this notification can be disabled.

Mozilla's development efforts will continue with the "rapid release" cycle, but this extended support offering is meant specifically to allow corporate users to satisfy security and stability requirement testing.

The extended support release is a welcome change after Mozilla changed the release structure of Firefox in the summer of 2011. The "rapid release" schedule of incrementing major version numbers between releases was meant to keep the releases fresh and allow addition of new major features. When the policy was announced, enterprise administrators rebelled, citing the need to conduct thorough testing before new major versions could be implemented throughout an infrastructure.

This move should placate most of the naysayers by providing sufficient time for administrators to test and implement the new browser versions.

For more information, including further details on the release schedule, you can see the official Extended Support Proposal on Mozilla's wiki.