text sizing in ems IE v Mozilla

[Ferellie]

I use 62.5% as my font size for the body.

I then use ems to size my h1s etc and my divs.
I heared somewhere that I must only use certain sizes in ems to ensure that ie and mozilla render them the same size, especially the headings.

I cant remember where it came from?
Can you shed any light on this as I really do prefer using variable font sizes everywhere.

Thank you.

[Twey]

I really do prefer using variable font sizes everywhere.

Good
IE seems to have trouble with font sizes under 1em, and displays them rather inaccurately. Apparently, using percentage font sizes to achieve the same effect rectifies most of this.