Rated 2 out of 5 stars
Pros: Makes functional APNG files! Customizable frame display times right to the millisecond.
Cons: This isn't something that would typically present itself as a web browser plug-in. Lacks ability to select frames to apply changes across multiple frames. Lacks ability to rearrange/insert frames. Runs slow. Appears to be a 16MB file size output limit.
Overall: APNG Edit has a long way to go, and it can only get better, but for the time being, APNG Edit is a good choice, if not the only choice to author APNG files.