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.

Sure. In one sense, anything is "modern" if it's developed this year, regardless of its feature set. So modern is probably the wrong word.

But the argument that a version of IE which hasn't even come out yet doesn't have features that other browsers have had for years are valid points.

I guess "IE9 sucks" was deemed not to be tactful enough.