As long as your PC is not locking up, and works ok, you can't be obsessing over 'why is my CPU or one of it's cores at 100% useage when at any particular website'....

Facebook is a near constant stream of content with near real time constant updates, is not a static website that is loaded and 'done'...

Possibly much ado about nothing, we will hope...
 

acer0169

Distinguished
I asked if they're running FireFox because as much as everyone seems to love it, there is (or was) a huge bug where it randomly corrupts itself and runs at 100% after a few minutes of use. Only way to fix is reinstall. Facebook - even as a large and constantly refreshing website - doesn't (or shouldn't) use any more CPU than a normal website.

Give us a bit more information grandmasjoys and we'll be able to help.