Firefox on Linux renders some ChatGPT emoji as monochrome outlines

 "font-variant-emoji",
 "emoji",
 "important"

   font-variant-emoji: emoji !important;

I have reproduced a persistent Firefox/Linux emoji rendering issue in ChatGPT and found a small CSS workaround that fixes it. Environment Linux Firefox 155.0.1 The problem also reproduces in a completely fresh Firefox profile Noto Color Emoji is installed Symptoms In normal ChatGPT conversation text, some common emoji such as: 😄 😂 😀 😁 🙂 😊 🤣 ✅ render as monochrome or outline glyphs. Other emoji such as: 🚀 🔥 ❤️ may render correctly in the same message. A particularly useful clue is that the same affected emoji render correctly inside ChatGPT code/copy boxes, while failing in ordinary response body text. Firefox DevTools Fonts inspection showed ordinary fallback fonts including DejaVu Sans, FreeSans and Nimbus Sans being used alongside Noto Color Emoji. Updating Firefox from 155.0 to 155.0.1 did not fix it, and neither did creating a completely fresh Firefox profile. Diagnostic test Running this in Firefox DevTools Console on chatgpt.com immediately fixes the affected emoji throughout the page: document.documentElement.style.setProperty( "font-variant-emoji", "emoji", "important" ) Permanent workaround Using the Stylus extension, scoped only to chatgpt.com: html { font-variant-emoji: emoji !important; } This survives a complete Firefox restart. This appears to be a font/emoji-presentation interaction where some emoji-capable Unicode characters are being satisfied by ordinary monochrome text fonts before the colour emoji font is selected. Mozilla Bug 1971053 describes closely related glyph-selection behaviour and mentions font-variant-emoji: emoji as a remedy: https://bugzilla.mozilla.org/show_bug.cgi?id=1971053 I am posting this both in case it helps other Linux/Firefox users and to ask whether this remaining behaviour on Firefox 155.0.1 is expected or should be tracked as a current Firefox/web-compatibility issue.