This add-on is similar to "Switch Container", i.e., it switches the current tab's container to the chosen one. The problem is the switching is not smooth, for some reason, it's visible that a new tab pops up, with the proper container, then the current one is closed. That process is, actually, the only way to switch container, currently, but the switching is unnoticeable on other switching add-ons. Another problem, the add-on messes the add-ons manager page (about:addons becomes unusable if "switched"...)