The SVG image referenced by an <img> element in this section https://svgwg.org/svg2-draft/painting.html#TermCapShape shows the text with a serif font despite the font-family="sans-serif" in the document. When I view the SVG document by itself, the text correctly is rendered in a sans serif font.
See also: bug 73153, bug 87069. Are these all the same thing?
Bug 87069 is definitely the same thing, since that's this bug. ;) But yes this seems a clear dupe of bug 73153. *** This bug has been marked as a duplicate of bug 73153 ***
Oops! The other one was bug 68090, which is likely related, but not quite the same.