(On Windows anyway, don't know if different on Linux)
Just wanted to share that as a user of both Firefox and Chrome, it's one thing that makes me hate switching to Firefox. I often need to use two different profiles and the way Firefox does it sucks.
With Chrome I've got two shortcuts (that Chrome creates by activating an option) pinned to my taskbar that look distinct from one another and the instances that I open are combined under their respective profile shortcuts.
With Firefox I need to manually create two shortcuts, assign two distinct icons to differentiate them, change some properties so they open the right profile, pin them and because they're "regular shortcuts" instead of the default Firefox launcher shortcut, when I open the program I end up with a third Firefox icon in my taskbar (it does not open under the shortcut I used, it acts as if I clicked a shortcut on my desktop) where all instances get merged together no matter which profile they're associated with.
If you set "always open this site in this container" then it always go to that container. If you don't set that, now you have select container every time. It becomes very easy to login inthe wrong containers.
If combine that with profile switchers, you get the best of both worlds.