That's CSS animation. There's a blog post from Surfin Safari dating back to 2007 for CSS transition, and a Mozilla article dating back to 2009 (might have been implemented before that)
The only thing I see in 2007 about this is an announcement that they're going to do it. Can you find a pointer to the blog entry announcing that it is available?
> We have another cool new CSS feature to talk about: animation specified in CSS. There is a lot of ground to cover here, so we’ll start with the basics first.
There are two technologies here, though both sometimes use the word "animation" they're separate: they implemented transitions in 2007 (using transition-* properties [0]), transitions are used to smoothly go from one state to an other and they are implicit: you only say which CSS property will transition and over which duration and the browser will handle all the decisions within that scope.
CSS animations[1] were added in 2009[2]. They are related to transitions but they're explicit and keyframe-based. Much more complex, but much more flexible as well (for instance you can have back and forth movements with animations, but not with transitions).
And even then it was just a proprietary vendor extension. It's not like it was part of the draft standard at that tmie.
If MS adds a new feature to IE, does that start the clock on when everyone else needs to implement it?