Despite not supporting them, it seems to show them up perfectly fine on my screen whenever I view them. Well, PNG files at the least. I don't know what alpha transparency means, but if it's anything to do with transparent backgrounds on gifs etc, then it works fine for me. Having said that, according to edc, Firefox doesn't work well with animated gif files. I would rather a file actually work well and not be supported than have a file supported but not work well.