I disabled font hinting in Gnome tweaks, but Firefox sometimes (for certain fonts I think) ignores that and tries to align glyphs to pixel grid, resulting in uneven spacing between letters and/or distorted glyphs. I'd like to force Firefox to never use hinting, if possible, are there ways to do so?
An example of bad font rendering (this is a line from gmail web interface where it shows the list of threads; there are extra spaces between letters in some places where they should not be, in particular "release" reads as "relea se"):
Firefox 64.0, installed from Ubuntu repositories via apt as usual, Ubuntu 18.04, with all recent updates. The display is not HiDPI, it has "regular" pixel density.
I tried to change font hinting by moving fontconfig files as described here https://askubuntu.com/a/29834/351113 (but used the
/etc/fonts/conf.avail/10-hinting-none.conf as the source, of course) and it didn't solve this issue (after clearing Firefox cache and reboot)
Just to check it with something really obvious, I tried to disable font antialiasing in Gnome tweaks (which makes fonts obviously hideous) and it doesn't change font appearance in Firefox, so I'm pretty sure Firefox ignores Gnome font settings.
~/.fonts.conf with the appropriate contents also had no effect in Firefox.
As suggested in comments, I tried Firefox ESR and it is affected too.