I'm not sure if this applies, but I really hope they provide better tools to identify badly behaving webpages. Sometimes when my CPU or memory are being cranked by Firefox, I really just want to kill the one tab out of 50 that's causing all the problems.
That isn't currently a target area for FHR. Things pertaining to the performance of particular webpages and such are extremely difficult to tease out of the data in a meaningful way. Not to say we will never include something like that in FHR, just not in the first couple of revisions of it. Have you tried out the about:memory page? It doesn't do CPU, but it is a good way to see what particular pages are hogging memo…
It seems to me that you could do this "well enough" if you put each page in its own process and let the OS tell you which are burning the CPU. There could/would be edge-cases where a page causing issues would not appear like it was causing issues, looking at it from that level, but it would sure as hell be a good start.