Containers are one of those features that I use almost in every Firefox session. It clearly segregates my office and personal work. I am asking for a feature, but there is all possibility that that might already exist somewhere in the advanced configuration (about:config). If so then please do let me know.
Before asking let me set the context. Before containers, I used profiles to separate my work. But the disadvantage of profiles is that the cache, auto-fill, history, bookmarks etc., all those convenient features are not the same everywhere. But the advantage of profiles is that every shortcut key, clicking of link would open in the same work profile. I don't have to open context menu (using mouse) and select a profile each time. Of course, I have done some advanced configuration and set control+shift+[1,2,3,4] etc. shortcuts to my different containers. But even that is not convenient, when I receive some office email with a link. That link opens in "non-container" tab; not what a user might want.
"Container Windows" could be such a feature which is best of both worlds. I am not aware if this is already there. At least the feature is not obviously visible. There is a feature in "multi-container plugin" which can move all the tabs belonging to a container to a separate window. if we add a feature, in this plugin or Firefox core, to bind a particular window to just one container then it can bring all the goodness of "profiles" and we can still use all the features of "containers".
1. Clicking a link in other application (emacs, thunderbird, etc.) would open the default container (no-container) window. No behavior change.
2. Control+Click, by default, opens tab in a bound container window, and hence in the same container. All shortcuts like control+t will also open Tab in the same container.
3. Context menu in all windows (bound and unbound) still gives an option to open tab in another container