No way to change system-ui font
Using Firefox, twitter.com's css uses the following font-family css to set font for text:
system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Ubuntu, "Helvetica Neue", sans-serif;
This results in text being rendered in Cantarell. Using Tweak Tools to change fonts doesn't change this, either. Ideally I'd like this font to track whatever was set in Tweaks->fonts->Document Text.
Edited by Ghost User