I imagine it is relatively well known that browsers handle text differently.
Really the biggest shift I see in a layout is the text rendering when it comes to firefox. The fonts are generally always larger and the line height is generally always larger.
I set fonts sizes, letter spacing and line height using em's.
I have looked and don't really see any good solutions.
There is some literature out there recommending setting the height to like 100.1% and then setting the fonts off of that.
But it is still consistently off.
Thanks for your time.