Same here. The way I noticed the slowness was that I am used to opening up a new tab and immediately typing in my url or search. Whatever speed comes naturally to me, Chrome can handle it. Firefox would lag in ways that resulted in half of what I typed being cut off and other odd behavior. I am positive that Firefox is (or was, when I tried it last year) slower than Chrome in this regard, which was incredibly frustrating and caused me to switch back to Chrome within a week.

There are a couple fixes in 63 beta specifically about OS X performance. https://www.mozilla.org/en-US/firefox/63.0beta/releasenotes/

> On macOS, WebGL power preferences allow non-performance-critical applications and applets to request the low-power GPU instead of the high-power GPU in multi-GPU systems - https://bugzilla.mozilla.org/show_bug.cgi?id=1349799

> Faster tab switching in the majority of cases for our macOS users - https://bugzilla.mozilla.org/show_bug.cgi?id=1481519

> Improved the reactivity of Firefox on macOS - https://bugzilla.mozilla.org/show_bug.cgi?id=1265824