[paularmstrong]

The images will always need a network request, but the non-JS version requires another request for the new HTML source.

And with the previous implementation, all users would get the progressive enhancement, not just non-Firefox users.

[jakelazaroff]

Compared to all the new icon images on the page, that request for the new HTML source is probably negligible.

With the previous implementation, all users would get the progressive enhancement… except non-JS users :) https://www.kryogenix.org/code/browser/everyonehasjs.html