Are you referring to Firefox's multi-account containers extension?
Sandboxed tabs is brilliant.
I just wish they added better overall profile support.
You can send a few tabs through one socks proxy, a few through another, all while segmenting that from work, personal, etc. if you have a vpn for one work location and different ones for other work.
It's amazing how well it works!
I just set a few glob rules on the URLs I need proxied and I don't have to think about it anymore :)
1. https://addons.mozilla.org/en-US/firefox/addon/facebook-cont...