It can be pretty difficult to wrap your head around the concept of matrix transformations. To debug matrix differences across web browsers, I made a nifty matrix sandbox page to play around with the numbers and see the effects in realtime. Just drag the sliders around and see what happens to the square in the middle.
A while back I needed to demonstrate how Flash's WMODE settings behave across all platforms and browsers. Instead of trying to explain it in words, I made a standalone test page that illustrates several key concepts.