Quite likely this is because Firefox 68 didn't support subpixel positioning so it aligned all glyphs to full pixels. Chrome 80 (and Firefox 76 in some configurations, or if gfx.text.subpixel-position.force-enabled is enabled) uses subpixel positioning if possible, which improves kerning of normal fonts, but in the case of these "retro" fonts, it's harmful. Maybe it's possible to adjust the glyph metrics so they're aligned to full pixels even if subpixel positioning is used, but I'm not sure if this can be really be done so it works everywhere.