Firefox hint issue when editing text in Roboto font. How to fix it?

When I edit text on some web pages in Firefox the some of the characters are slightly moving around their original position. Each time I type a character or move the cursor or hit delete or BS, the spacing of some character in the text is slightly adjusted. As a result, some characters are kind of "shaking" while I type which bugs me.

Chromium behaves perfectly well on the sames pages.

This issue occurs for instance when I am on my NexCloud pages.

I have Kubuntu 20.04 and Firefox 82.0(64bits) but I noticed this for quite some times now with former versions of Firefox and Kubuntu. I have the same issue on another computer with a relatively fresh install of Kubuntu 20.04.

I thought I would find some posts about it but apparently nobody was bugged enough to post.

Solution 1:

After some tests with fontconfig, I found a solution by disabling full hinting on Roboto font.

In /etc/fonts/conf.avail/56-kubuntu-noto.conf replace :

<edit name="hintstyle" mode="assign"><const>hintfull</const></edit>

by :

<edit name="hintstyle" mode="assign"><const>hintmedium</const></edit>

You must quit your session and reconnect for the change to be effective. I am not a fontconfig expert. Maybe there is something better to be done, but it works for me. Since this file comes from the kubuntu-settings-desktop package, I assume this is a Kubuntu only issue.