The font rendering on the mozilla website is absolutely horrific (Firefox 68/Windows 7): https://i.imgur.com/JMpq9Xe.png
gfx.font_rendering.cleartype_params.enhanced_contrast = 0
gfx.font_rendering.cleartype_params.rendering_mode = 5
gfx.font_rendering.cleartype_params.force_gdi_classic_for_families = ""