ColdFusion and PDF font-size pt vs px

So a few months ago I was walking by a developers desk and stopped when I saw him frustrated with some ColdFusion PDF output. He was working with font size's in using pixels (Ex. font-size:15px;) and it was not rendering the same in FireFox and IE. I sat down with him for a bit and we both thought using pixels instead of points (Ex. font-size:15pt) would be compatible across browsers. Our idea was wrong. I went back to my desk and played around with the compatibility of different pixel sizes in the two browsers but had no luck. Giving up with the pixel's idea, I then tried pt. Using pt worked far better then px when dealing with PDF.