Earlier quoted context omitted.
Arc is much more than that, though. 1st. Tabs are both tabs and bookmarks. They exist to be more or less persistent (as long as you add them to folders - I get it, it's not everyone's workflow, but for people like me, it's a blessing). 2nd. It has a brilliant tab sync between devices. Something Firefox doesn't do - in fact, only Edge does that. 3rd. Is much lighter on resources on macOS. Some months ago I decided to…
You can open tabs from other devices in Firefox. They don't open automatically though, presumably because some people (i.e. myself) would find that horrible.
That, together with clearly defined workspaces, is fantastic for me.