github.com/GrapheneOS/gra is the best solution I could come up with for bugs.chromium.org/p/chromium/iss without making things worse for Firefox, Safari and other clients. It also has the nice property of making Chromium-based browsers use the SVG favicon for non-HTML pages too.
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SVG favicons are nice because you can change the colors based on whether the browser's dark mode is active. That's now supported by grapheneos.org in both Chromium-based and Firefox-based browsers. It works a bit better in Chromium-based ones since it works for non-HTML.
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The only way to improve that for Firefox would be user agent sniffing and I refuse to do that. It would be nice if they advertised support for image/svg+xml when fetching /favicon.ico. Chromium seems to always list out all the fancy modern formats when fetching any images now.