Er, how? Not seeing anything there that helps.
Also, Chrome already has an extension that allows you to view APNGs inbrowser.
@ aldeng, your doing nothing wrong, its just that animated GIFs/AGIFs don't tollerate transparency.
Note: This only applies to animated GIFs. If I remember right (been a while since I saved a file with transparency in GIF format) non-animated GIFs tollerate transparency.