Useful addon. The cues Firefox provides by default for current container are good but not enough. This addon fills what is missing. It makes it very obvious which container current tab belongs to. I am impressed that someone came up with this idea.

Though there are two issues, at the time of writing, which I hope @jkt will resolve eventually.

1. The colors are too bright
2. https://github.com/jonathanKingston/containers-theme/issues/1