We figured this one out, we have an experimental component on meta.discourse.org that added:
.buttons:has(*:nth-child(n + 3)) > button span,
.buttons:has(*:nth-child(n + 3)) .quote-sharing button span,
.buttons:has(*:nth-child(n + 3)) .ai-post-helper > button span {
display: none;
}
.buttons:has(*:nth-child(n + 3)) > button svg,
.buttons:has(*:nth-child(n + 3)) .quote-sharing button svg,
.buttons:has(*:nth-child(n + 3)) .ai-post-helper > button svg {
margin: 0;
font-size: var(--font-up-1);
}
Chrome is able to handle this somewhat gracefully, but on Firefox 121 (which just added support for has) performance gets pathological, especially if you are adding stuff to the DOM