Hmm, I didn't notice anything on Firefox on my Mac. I have a ton of tabs open and about and 15 programs running, including handbrake rendering some videos. I opened up Activity Monitor and watched what happened while loading and then manipulating the sliders. Nothing. Absolutely nothing budged under CPU, GPU, or Memory. The site was smooth as a hot knife through butter.

Maybe you should list your OS, your browser, and your hardware specs.