I agree that font rendering is fairly consistent. The problem is that a single pixel difference in vertical rendering can affect word-wrapping in such a way tha

I agree that font rendering is fairly consistent. The problem is that a single pixel difference in vertical rendering can affect word-wrapping in such a way that a new line is added, making the div taller, potentially breaking the page layout. One related thing I know for a fact is different between browsers is how they treat fractional line-height. While Firefox accurately scales the line-height along with a fractional font-height, Chrome notoriously snaps the line-height to an integer number.