I love it, for a while now I have been using Firefox containers and they're especially handy. It's a shame that this functionality isn't included in the official Multi-Account containers extension or Firefox itself but this extension fixes it perfectly. My one request would be to have the container options in the right-click list at the top of the list with "Open in New tab" and "Open in New Window" but that might need to be implemented on Mozilla's end.

EDIT: I saw Rob's response to an earlier review and it seems like Mozilla is starting to implement this feature directly into their Multi-Account Containers extension BUT it's not as feature complete as this extension