Mozilla Connect

@BenDC-iconicit @flalumiere Figured it out. Click the Firefox Multi-Account containers extension (not the always open site in container button in the URL bar, but the extension icon in your toolbar or under the Extensions menu), then Manage Container...

I also don't see any way to rearrange on macos either in the new tab right-click menu or in settings → container tabs. How do I do this?

+1. I think Doppelganger's idea above is a great possible implementation.