It's not that Firefox isn't an excellent browser on its own, but on macOS Safari rises the bar very high if you care about details (most people don't).
I disagree with this. Safari and Chrome are both noticeably better than Firefox on OSX.
I'm a Firefox fanboy, still use it on OSX because it's important to me, but the amount of random pauses, crashes, etc is just painful on OSX. It's like none of the Firefox developers use it on OSX or something.
And before someone says "oh it's your extensions", that IMO leads to two talking points
1. It's 2020 and major extensions still cause memory leaks in Firefox. Debugging them isn't easy at all. Almost all of the resources say something like "Run in safe mode and see if it fixes things" and then lots of posts of "post your about:memory here and I'll analyze it." I'm a software engineer by trade and it's been difficult for me to diagnose...
2. Nah because I don't run any extensions on my OSX firefox install
Well, at least for me, Safari is often still the fastest browser and has long been the best at power management (important when you're running on battery power). And I like its UI a little more; its tabs, for instance, are native macOS tabs. Firefox and Chrome both make up their own stuff.
As far as "least standards-compliant," I understand that when it comes to supporting progressive web apps, Safari has largely dropped the ball, but in day-to-day practice there just aren't many sites that I have trouble with on Safari. (The biggest one seems to be new Reddit, and I am not entirely convinced that issue is on Safari's end.)
Yes, Safari is the most buggy browser in common use other than IE11. It's also the one that uses the least battery life, it's standards-compliant enough to render most web pages, and it's the only option on iOS.
It's somewhat a myth that Safari is less standard-compliant. True, Safari's release cycle is slower and Apple has the motivation to prevent PWAs to become too good, but in many things Safari has always been very innovative browser.
Built on top of KHTML foundation, it then became webkit and later the most successfull engine. It was the first to implement full ES6 support, and basically invented CSS transformations/transitions (really amazing stuff back then but not really used until all major browsers caught up years later), was the first to ditch Flash support, has argueably the best privacy policy, has superb font rendering, etc.
Internet explorer is also a very innovative browser. It introduced XHR and a bunch of other stuff. But that is a different measure from standards-compliant.
Yes, IE was very innovative in its heyday (up to version 4). But back then there was no strong standard body (sort of status quo) like we have today, and due to Windows monopoly they could come up with stuff which was never even intented to be implemented by other vendors (well, Mozilla). You cannot really compare that era to today's situation.
