I think it is reasonable to expect that the help pages will include a good description of the extent of Firefox CSS3 support.

I am interested in using CSS3, especially the ability to load fonts when needed off the internet. I would therefore like to know the extent of Firefox support for CSS3. I couldn't find any pages in the help system answering this directly. There were a number of bug reports going back in time (so clearly there is some support) but the definition of the facilities was not there. This is very much needed because browsers commonly only implement a small subset of the facilities defined by W3C, so it can waste a lot of time to start with the W3C specs.