Flamingo already has it I believe?

When I was onboarding nostr:nprofile1qqsfaw4qdnt7rhxvcwv6yvqcz2gzmt3xup5n4daesspe3vdxnv2yu5qpzdmhxue69uhhqatjwpkx2urpvuhx2ue06yqv9v (he needs to use Nostr more!) I showed him one that worked with Opera, his browser of choice, and it had multi-account options

I was pleasantly surprised