Why does FireFox have different font sizes on different sites?

Question

Fonts

Available:
- Windows 10;
- scaling - 125%;
screen resolution - 1920x1080.

FireFox settings:
- version: 87.0;
- font size: 9;
- scaling: 90%.

Question:
Why, when opening different sites, the font sizes are somewhere smaller, somewhere larger? Previously, there was Ubuntu 20.04, which did not have this problem.

Click to see screenshots

UPDATE:
Just installed Chrome Version 90.0.4430.72 (Official build), (64 bit) - no problem, everything is displayed well.

Answer 1

Perhaps it's the useragent
and depending on the UA the site gives certain font settings,
try changing the agent in firefox to chrome
about:config
general.useragent.override
string
insert your value
https://developers.whatismybrowser.com/useragents/...
perhaps this will solve the problem, but it is also possible that some extensions may not work correctly.

Answer 2

Jake Taylor , just try to increase the font size in the settings, section "Language and appearance".