К сожалению, не работает. Ни 56 версии, ни в предыдущей.

Every single site I visit, the plugin shows a red "X" indicating that it doesn't seem to be working at all. On Firefox 56.0, so I'm not sure if that's the issue or not, but I imagine not.

Using Mozilla official addon and cookies inside those tabs aren't touched. Please add support!

https://addons.mozilla.org/firefox/addon/multi-account-containers/?src=userprofile