NOTE: I am answering my own question, since I was not able to find any reference here in SE to this particular bug on which I stumbled upon and found the fix accidentally. Hope it helps someone . . . . .
<!-- some comment-->
<! DOCTYPE html>
. . . . .come css3 stuff here
The above html works perfectly in Mozilla and Chrome . . .But, why it is not working in IE9?
ANSWER:
In IE9, document declaration should not have any comments before them, apparently. The following code will work in IE9
<! DOCTYPE html>
<!-- some comment-->
. . . . .come css3 stuff here
I don't know why this is the case, but I was breaking my head over this issue, as I have some other files working perfectly in IE9 (they didn't have comments before doc type) . . .I reinstalled IE9, finally found this issue . . .
Hope it helps . . . .