Strange. I've been using Firefox on macOS for the last 10 years and it's still working well for me, including to access Google services.

Tabs work very well in Firefox for me. I have 17083 tabs open at the moment, on my 2013 Macbook Pro, still going strong.

The Containers are great for separation of concerns and for multiple accounts like work vs personal, business shopping vs personal shopping, etc.

I tried Safari for a while but switched back to Firefox. I use Ungoogled Chromium occasionally to generate PDF invoices and have used it for a better Google Hangouts experience, but otherwise rarely open it

I have no idea if the situation has changed there, but in the early 2010s when I worked for Mozilla there was an ongoing issue where Windows was the less exercised platform internally because almost everyone had a MacBook on their desk.

huh? My main browser is FF on macOS. I currently have ~350 tabs open across multiple windows. I have zero bugginess.

I consider Chrome primitive because it lacks vertical tabs (kinda necessary with >10 tabs open at once). You can't even get workable vertical tabs with an extension on Chrome!