I am aware that threads don't run continuously; scheduling just makes this worse just like timer jittering does. Sadly, I'm not the kind of person who can drop full, working exploits against unpatched browsers in response to Hacker News comments; I just have a passing interest in the field :(
<<you can busyloop and count iterations of that instead as a “timer”>>
Assuming you're the only job running on the CPU, which is not the case. Threads are not running continuously. But again, if there is a working exploit in the browser then show us. Talk is cheap.