I nearly doubled my battery life on linux by zooming on facebook until the chat bar on the right hand side disappeared. Didn't even need to close the facebook tab, just that bar was keeping the CPUs running hot. That's been effective enough for me not to bother with decent trace tools just yet.
I do use the chat though, and every time you click on the chat it brings back the sidebar and requires clicking a tiny icon and a menu option to get rid of it again.
Little-known tip (I think): messenger.com offers a web UI for Facebook chat similar to their iOS/Android apps, also ad-free and significantly cleaner than the actual Facebook UI. No idea whether it's actually better on power consumption though.
