There are some differences in how engines render text Chrome’s engine by default renders fonts visually “bolder”, especially on some specific font sizes (some webdevs might choose to mitigate this, most don’t) effect also depends on specific font in use
I’m afraid if that’s what you mean you can’t really “solve” it…
For a test, can you screenshots this page (with hardcoded different fonts than default Liberation sans at least for headings), i’d like to see how it renders for you side by side
It seems the “conf.avail” directory no longer exists:
…and I found this entry in the Arch-Wiki wich is new to me:
Note: For some desktop environments (such as GNOME and KDE) using the Font Control Panel will automatically create or overwrite the user font configuration file. For these desktop environments, it is best to match your already defined font configurations to get the expected behavior. Also ensure that the desktop locale settings or Regional Settings are supported by the configured fonts, if not the font configuration could be overidden.
…and further this one
Note: Configuration files and directories: ~/.fonts.conf/ , ~/.fonts.conf.d/ and ~/.fontconfig/*.cache-* are deprecated and will not be read by default in the future versions of the package. New paths are $XDG_CONFIG_HOME/fontconfig/fonts.conf , $XDG_CONFIG_HOME/fontconfig/conf.d/NN-name.conf and $XDG_CACHE_HOME/fontconfig/*.cache-* respectively. If using the second location, make sure the naming is valid (where NN is a two digit number like 00 , 10 , or 99 ).
After deleting the (now broken) link @keybreak suggests my font rendering is OK again.
Again there must have been something modified in this fontconfig mess
If problem is caused by fontconfig changes - it’s not only Firefox but any program that use fontconfig directly (many people complained about it because everyone use browser therefore start to identify it as Firefox problem, you can search forum to see all those topics)
If it’s something else that is caused by Firefox only, like engine rendering differences - then it’s only Firefox and your advice is very relevant, it’s good idea to experiment with values