I've just started noticing in Firefox 99 on Arch Linux that Firefox is using the wrong font when the font-family is given as "ui-monospace/other fonts..., monospace". This looks similar to the issue mentioned here: https://support.mozilla.org/en-US/questions/1351497 The inspector for these websites underlines "monospace" as the active font, but then uses a non-monospace font (in my case, Bitstream Vera Sans) to display the content. This does not happen when the font-family is "monospace,monospace" or "monospace". I can't quite figure out exactly what causes the font to be chosen incorrectly: sometimes it does show up if I have the preceding fonts installed, e.g. Consolas or Liberation Mono, but other instances do not look as intended. Currently, I have fontconfig set up such that: $ fc-match :family=ui-monospace VeraMono.ttf: "Bitstream Vera Sans Mono" "Roman" $ fc-match :family=monospace VeraMono.ttf: "Bitstream Vera Sans Mono" "Roman" Firefox's fonts in about:preferences are configured as all defaults: Serif: Bitstream Vera Serif Sans: Bitstream Vera Sans Monospace: Bitstream Vera Sans Mono