Mozilla set big expectations for this extension, but it did not work at all in Firefox 84.0 for Mac. I installed and enabled it, but the add-on's icon never appears in the toolbar and right clicking on web links does not present an option to choose a container. In the manager for the add-on, I created new containers in addition to the defaults and they disappear as soon as I exit the manager and re-enter it. A perpetual warning message appears in Firefox's Preferences indicating "An extension, Firefox Multi-Account Containers, requires Tab Containers," as though they are not enabled and need to be. Yet the checkbox for Enable Tab Containers right below that warning is enabled. So tab containers appear to be enabled, but the add-on is completely non-functional and worthless, and there are no help articles that address the problem of the icon not even showing up and no container-choosing functionality appearing after install. Mozilla set big expectations or this add-on and delivered a big disappointment.