Same observations here.
It's better on win 7 (compared to win XP), but still yes, stuttering.
Let's wait and see if the next versions of FF will correct this. Games are still playable, nevertheless, and we know it's browser based.
We will just have to let the users know what browser offers the more comfort/performance in the end and inform them that they should use that browser.
Nowadays, it is not a big deal having two browsers, one default for navigation, and one other for "alternative use".
I think I'll stick to FF for my everyday navigation, and use chrome for all that is gaming.
Previewing anyway in chrome and FF (even if I still have that strange bug that doesn't allow me to launch the preview on the browser chrome, even if it is installed. I copy the preview url to a blank chrome window and it works.)
I'm confident webgl renderer should allow for particles easier/steadier.
WebGL, despite the right-clicking, is steady and non-stutering in FF (at least from what I've seen so far).
Reminder Scirra's blog post about HTML5 performances from mid November.