Comment 16 for bug 902594

Note that the bug was duped onto bug 1103102. In any case all of those bugs have no clear-cut context explaning *when* CPU is running unexpectedly. In all cases the deciding factor causing the issues is unknown.

As an example there used to be a JavascriptCore bug which caused high CPU usage when closing a website at the wrong point in time, the work-around being to re-open the exact tab, that is to say it was a race condition within WebKit. It would occur in particular on stackoverflow and askubuntu.
If you can narrow down what you're seeing similar to this I would highly appreciate it. Otherwise there's nothing I or anyone else can investigate.