CPU at 20%, "loading didn't make too much of a difference"??? 20% is obscene for a process without interaction. Imagine a paused video player taking 20%, or a minimised word editor. Even at 58 videos or documents.
Firefox is working on this. Doing it without breaking things like music streaming sites is ... delicate.
Earlier this year I realized a major offender was Google search and search results pages which would spin up a core more than once a minute.
This explained to me at least why it was still hogging cpu even with ad blocker.
https://billmccloskey.wordpress.com/2016/10/27/mozillas-quan...
and a preliminary version is in Chrome 56: