Run challenge without Web Workers?

[otonoton]

If Web Workers are not available, then instead of showing an error message, can the challenge just continue without Web Workers? That way people won't have to change anything on their browser. Even if the calls are synchronous, it's not like the entire browser will freeze... only the page they're on, which they already can't interact with anyway because the challenge takes up the whole page and you're still waiting on it to finish regardless.