If this isn't a Mozilla product but Addon software you need to contact their creator for support and installation.

''<p>markwarner22 [[#answer-1720530|said]]</p>'' <blockquote>If this isn't a Mozilla product but Addon software you need to contact their creator for support and installation.</blockquote> Actually the "Firefox Multi-Account Containers" is one of the few Mozilla made extensions at addons.mozilla.org ''<p>mohammedomarduale [[#question-1501131|said]]</p>'' <blockquote>Firefox Multi-Account Container installation? How to do it and add on my page </blockquote> There is this KB article about Multi-Account Containers. https://support.mozilla.org/en-US/kb/containers