Hi,
The same site http://www.g-raffa.eu/Cinelerra/HOWTO/ (just as an example)
The same default font settings in Firefox.
Ubuntu MATE 18.04 beta
http://piccy.info/view3/12259940/700aeca66bcd0be17d0acab38369f4e6/orig/
Xubuntu 18.04 beta
http://piccy.info/view3/12259944/7a275e296c7f47afe034291b9ca8cd46/orig/
You see that the sizes of fonts are different. The font size in MATE is less than in Xubuntu .
Question: how to make the size of fonts on this site (http://www.g-raffa.eu/Cinelerra/HOWTO/) (and on other such sites) the same as in Xubuntu ?
Based on the back button and URL bar in your Xubuntu photo, it looks like the Firefox version in that photo is much older (before version 57 "Quantum"). I'd try comparing again after you make sure you are using the same version of Firefox.
[quote="elcste, post:2, topic:16488, full:true"]
Based on the back button and URL bar in your Xubuntu photo, it looks like the Firefox version in that photo is much older (before version 57 "Quantum"). [/quote]
It was Ffox 38 (GNOME 2) but it had the same size of fonts as in xubuntu
OK.
Xubuntu 18.04 BETA Firefox 59
http://piccy.info/view3/12262552/d3a3e1f0db1f72157af6314e42d63a75/orig/
http://cdimage.ubuntu.com/xubuntu/releases/18.04/beta-2/
It looks like they are different typefaces. They are similar, but the lowercase g uses different forms. This might also explain the size difference.
Comparing the packages listed in the .manifest files for the Bionic beta 2 of Ubuntu MATE and Xubuntu, I see that Ubuntu MATE has a few extra fonts installed:
fonts-arphic-ukai
fonts-arphic-uming
fonts-noto
fonts-noto-color-emoji
fonts-noto-unhinted
fonts-opendyslexic
fonts-tiresias
Xubuntu has one font that Ubuntu MATE lacks: fonts-symbola.
You could try installing those fonts and see if it changes it for you.