How's that?
Firefox is way better nowadays than it was a few years ago.
I have been using as my main work browser for some time and I don't face any performance issues with it.
On a BSD? It's great for me in Windows or Linux, but it's really choppy scrolling or watching videos in OpenBSD. There was a post on the mailing list somewhere that blamed excessive mallocs. This was with version 69, so not some ancient version either.
I've been running Firefox on OpenBSD on a Thinkpad X260, for about a year, and it's been working great, including videos and scrolling.