A few corrections: Sharing the AVM2 between Flash and Firefox will do nothing to "improve compatibility and stability with Firefox." If you have the Flash Player/VM on your system then you have Flash, end of story. There is no such thing as a Flash compatibility issue with FF, or IE for that matter.
Lastly, Flash is not under assault from AJAX. It's popular to think in terms of "my programming language is better than yours" but it simply isn't the truth. Both do similar tasks. Both are based off the same language - ECMA. Both are growing in popularity. Take a look at the job boards. There are gobs of job openings for both AJAX and Flash developers. Just because I'm a Flash developer doesn't mean that there's an AJAX developer somewhere out of a job. We're not competing with each other. Well, maybe a little. :-)
Xbox.com and Zune.net Flash Developer