/etc/fonts/conf.d/21-emoji-rendering.conf makes emoji rendering in Firefox worse

I’ve noticed that emoji look weird in (rpm) Firefox (look at those spooky triangle eyes!). After deleting /etc/fonts/conf.d/21-emoji-rendering.conf, emoji got rendered properly.

Other applications, such as Konsole and Chromium, don’t have this problem.

/etc/fonts/conf.d/21-emoji-rendering.conf says that emoji fonts don’t need hinting. It seems not to be the case.

My fontconfig file in home directory hasn’t specified hinting or hintstyle.

I’ve already filed a bug report on boo.

Have you guys encountered this problem?

System info:
Operating System: openSUSE Tumbleweed 20240423
KDE Plasma Version: 6.0.4
KDE Frameworks Version: 6.1.0
Qt Version: 6.7.0
Kernel Version: 6.8.7-1-default (64-bit)
Graphics Platform: Wayland

Firefox version: 124.0.2