Well that was a few hours of painful stepping through horribly cryptic javascript.
As you recall, www.stackoverflow.com referenced
https://js-sec.indexww.com/ht/p/185901-159836282584097.js
which in turn ran forever, and even ran forever on its own, outside the context of stackoverflow.com.
That's good I guess, it means I only had one file to slog through.

The problem was frameElement, which we never implemented. I didn't even know about it. (This is where the acid tests might help.)
Only took 17 lines, and there it is, and the loop goes away.
That's the thing though, js assumes our browser is perfect, and if it's not, there's no guarantee that js won't go off into an infinite loop.
It usually doesn't, but it could.

Karl Dahlke