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.
You may set 1 000 000 iterations in options but what these numbers show is what actually was calculated, in this case:
9951 of 10000 moves. If you set low time you will never get to 1 000 000, it will stop on the time.
You may look at the Help there are tips there.