@Matter Won't every i3-tab-firefox be its own session of FF and thus need its own profile? You can have more than one copy of FF going at a time, yes. If you're thinking about this for security reasons, are you already looking at/ruled out Qubes for better sandboxing/etc of your machine?
A nice little Mastodon instance. Mild trolling encouraged (keep it local), but not required. Malicious behaviour is not tolerated. Follow Wheaton's law and you'll be fine.