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/* UNCOMMENT BELOW to force a boring system font (might break some web icons) *Firefox already includes a better version of this: Settings → Fonts → Advanced settings → untick Allow pages to choose their own fonts, instead of your selections above.
It makes the web much better. Firefox even includes a list of icon font names that will be permitted (pref browser.display.use_document_fonts.icon_font_allowlist) to minimise icon font breakage, though I chose to block font loading altogether and there’s not often much trouble from it (and most of it is Google’s, and Material Icons’ ligation technique is in practice so dumb, achieving results quite the opposite of the original reason for the technique in an entirely predictable way).
> I need colors for code
Quite honestly, try doing without it for a while and see how it goes. Make a new theme that’s limited to just black on white, with regular/bold/italic font styles (me, I did keywords bold and comments and macro stuff italic and that was all), and use it for a week. Then consider if you want colours, and how to add them. Me, I went to strings red and comments green and numbers blue and not much else, though it’s grown a little over time. Others add greys, and perhaps background shading.