Uploading custom avatar on moz://a profile

The upload seems successful according to the json response in web console.
Yet the popup keeps the “Save Changes” button disabled.

Firefox Nightly 57.0a1 (2017-08-16) (64-bit) (Debian 9)

Which profile is that exactly? Mozilla has several different platforms where users have profiles. Would be good to know which one you mean, I’d guess mozillians.org?

Edit: nope, mozillians.org does not have a save button, so I’m not sure what you mean with “mozilla profile”.