[aibara]

I've used Firefox with Ubuntu for over a decade and have never had any issues with the fonts the OP mentions. Maybe it's a problem with some other distros, but I thought Firefox followed your system's settings regardless.

Chromium, on the other hand, has never fully obeyed the default font settings. Even messing with the flags there are plenty of times the font hinting would be different on certain sites than what I've set it too (e.g. grayscale instead of RGB). Never got into troubleshooting it too much though, since I don't use it as my default.