Firefox seems to have some threshold to leap to a larger font or a different font rendering scheme when adjusting the (Font) Scaling Factor in Ubuntu/Gnome Tweaks. Nothing happens in Firefox windows until the Scaling Factor reaches 1.25 (125%) and then it jumps to render larger fonts everywhere. (next jump at 1.4) See the screenshots for the difference. What is this threshold? What is the actual parameter Firefox reacts to?


I have asked the same question on Mozilla support website to no avail. So it seems I had better chances here as this regards Gnome specifically. You are welcome to check it though for more background https://support.mozilla.org/en-US/questions/1339647