I recently had some projects where the client wanted the page layouts and CSS tested in Firefox 1.5 and Firefox 2. I can’t seem to find any difference in the way Firefox 1.5 or Firefox 2 renders CSS. I haven’t found other blogs, forums or Mozilla help docs that talk about it either (though I’m still looking). Please reply to this post if you have any light to shed on the issue. For now I consider them to be the same when it comes to CSS.
In the process of my search I came across Mozilla’s CSS Developer CENTER. It has some essential links and good introduction to CSS. It also has some good info on CSS3 (which may someday be part of the day-to-day real world).

Mr Goldman,
Have you found any helpful info yet? It looks like you posted this awhile ago. I’m currently dealing with some difficulties…CSS is rendered properly in all FireFox browsers except 1.5. If you have come across any helpful resources, please send them my way.
With gratitude,
Justin (a.k.a. SureFire Guy)