If you don't like Firefox there are other programs that do Animated pngs. Kyria does use firefox but doesn't like the addin for making Apngs. So she uses japng-editor, a nice little java script apng assembly tool. it's freeware.
As Togan said really only one browser out of the many seems to show them correctly. SO if you do use them, you'll just have to be prepared for a lot of people not being able to see aything beyond the first frame.