>privacy enabling features of firefox that are served as extensions like the containers feature can suddenly and without warning stop working.

containers is a core feature of the browser. The addon (Firefox Multi-Account Containers) only adds some niceties like an addon button to start containers, and auto-assigning sites to containers. Without the addon, you can still manage containers by going to about:preferences#containers and open a tab in a given container by long pressing the new tab button.