It's quite the thing. I profiled it with and without ads, and it looks like the ads are the culprit. There are two of them just sitting there using CPU time the entire time the page is open. (I had two Facebook ads that had animated text being typed. They continued to use 100% of the CPU even when the animation was complete.)

There should really be some sort of CPU/power budget enforced by one's phone on a per page basis. If there's no user action going on, a page should only be allowed to run a certain number of instructions.