Nah, I was setting the iteration limit to 5000 like you said. Now I've also set the time limit lower. It plays quickly enough to be usable again. Too bad it's also weak like before.
Now it consistently thinks for about twice the time limit, which is perfectly fine, but I can't set the iteration limit that high because it starts freezing my browser again. And even at 150K iterations it doesn't seem any smarter than at 5K.