APNG (animated PNG) images support [Firefox and Safari 8 support it]
APNG is an extension of the Portable Network Graphics (PNG) format, adding support for animated images. It is intended to be a replacement for simple animated images that have traditionally used the GIF format, while adding support for 24-bit images and 8-bit transparency. APNG is backwards-compatible with PNG; any PNG decoder should be able to ignore the APNG-specific chunks and display a single image.
GIF vs. APNG vs. animated WebP: http://littlesvr.ca/apng/gif_apng_webp.html
Support status: http://caniuse.com/#feat=apng (Firefox and Safari 8 support APNG)
APNG support can be easily introduced with a very little additional code. Please consider it, this is just two week job for one developer.
There are many APNG files already in the Internet, even on Wikipedia!