[avian]

I think you underestimate how widespread ESR Firefox is.

Debian ships Mozilla's ESR releases by default. I'm sure many shops that prefer stability over latest features also deploy ESR. Judging by how often it gets updated it seems to me Mozilla is pretty diligent at backporting fixes.

My wholly-not-representative-for-the-wider-web statistics say approx. 22% of Firefox UAs are ESR release.

[akerl_]

If 100% of the user pool for Debian, including all derivative distros (Ubuntu, etc), plus all users of the Tor Browser Bundle all used ESR Firefox, that would still make it a blip in the overall body of user internet traffic.