I would love to use Firefox for it's privacy credibility, the Awesome Bar and to prevent monopolization of the Web.
Unfortunately 2017 is the year of the CPU usage apocalypse on the Web. Go to this insane Guardian page, scroll down a page, and observe what happens for a minute or two perhaps scrolling down some more: https://www.theguardian.com/news/2017/aug/10/adele-vocal-cor...
The numbers keep jumping around a lot, but very roughly what I'm seeing is this:
Safari: 2% - 8%
Chrome 50% - 150%
Firefox 150% - 250%
(100% is one CPU core. I'm not using any ad-blockers)
Obviously, these numbers are non-deterministic and depend on the individual ads that are being displayed. But the numbers are roughly representative of what I've been seeing over the last couple of months.