I have a vague memory of the browser icon having the name “Internet” back in the day. Or maybe it was the dial-up icon. Might be that?

Feels like jellyfish fits perfectly (if we ignore the whole can’t be on land stuff).

Does Firefox multi-account-containers work for you? Not on a desktop atm. but maybe you still need to have separate windows for that…

Anyways I’d still highly recommended the extension!