I think your question makes more sense if you broaden the idea of "browsers" a bit. wget? It barely "supports" html; it has a parser because it can follow link

I think your question makes more sense if you broaden the idea of "browsers" a bit. wget? It barely "supports" html; it has a parser because it can follow links, contrary to e.g. curl, for which "HTML" is just a stream of bytes really. that tv-thing hanging in the underground or the bus rotating awkward advertisements, local weather and public transport info? It might very well use some minimal rendering engine that only knows barebones of HTML? this thing in the set-top-box on the TV that gets "broken" HTML from some server and presents the buttons and such? same there. I presume if you are liberal at what you consider "a browser" it makes sense that several will not support that element.