@kravietz That's interesting, thanks! I spent some time on their website and read https://www.ekioh.com/blog/improving-html-browser-layout-performance/ : "The CPU intensive operation of laying text out in paragraphs is particularly suited to parallel execution. On a page of text, nothing in one paragraph affects the word wrapping of the others, just their vertical position."

Now I wonder if #LaTeX and #TeX could also benefit from such techniques. I feel like they are all single-threaded at the moment.