Except that they responded to none of the real concerns with IE9 being labeled as a Modern Browser, and instead listed off the same marketing drivel we've been hearing from their camp for the past year.
Yeah, Mozilla's argument seems odd. It is basically saying that IE9 is not modern because it is about on par with their shipping browser (FF3.6x) -- and lets not forget that IE9 has a better UI, better tab isolation, JS perf, and rendering perf than FF3.6x. If anything Mozilla should immediately urge all FF3.6x users to move to Chrome.
I think a more true, yet less controversial statement from Mozilla would be, FF 4 will leave IE9 (and FF3.6x) in the dust with respect to standards conformance.
I'd even agree with that. But saying that IE9 is not modern seems dishonest.
I agree with you that they are trying to be classy. The problem is that they are just plain wrong and they have no supporting evidence besides 'OMGZ WEB SOKETS.'