I think Firefox multi-account containers were at some point slated to have per-container proxy settings. This should allow each container to use its own IP address, with the help of either a proxy provider or a set VPN connections with local proxy servers.

I wonder if said functionality has been implemented, and if so, whether anyone has taken advantage of it to make per-container addresses easy for casual users.

Doesn't Safari's private browsing mode, combined with iCloud Private Relay, do the same?