Pretty useful. Something I learned at some point was that you can actually combine this with Wireguard: If you dig into the extension, there's a feature that lets you set a SOCKS5 proxy for a profile. You can then point it to a running Wireproxy to go from SOCKS5 to Wireguard. Could be handy.
Accessible via the UI: click into the extension, click the right arrow next to a container, select "Manage This Container", then "Advanced Proxy Settings" and you can enter a SOCKS5 URI. And of course, this requires the aforementioned extension, not just the built-in container tabs feature. (Confusingly, Firefox does have this feature "cooked in", presumably they just expose a bunch of it via WebExtension APIs so that things like Multi-Account Containers can work.)
