A few years back, I had written a simple page that made most browsers sluggish, folks. It was intended as a benchmark, but I was still surprised at how hard some took it.
I can't exactly recall which performed how, but initial load and reflow on window resizing could take many seconds. Today, none of the 3 engines in widepread use (Safari's WebKit, Firefox's Gecko, Chrome's Blink) have any issue with it.
However, I once again find myself bringing Blink to a grinding halt. This time, visiting pages like Mathematics on Wikipedia, with custom CSS, in an 8K window. Sure, it's niche. Nice problem to have, I guess.
Safari, on the other hand, loads and reflows smoothly. Looks great, by the way (besides sans-serif not mapping to my favourite font, PragmataPro):
