Also, you can backup/restore/move profiles independently of each other.
Also, you can have different network settings for different profiles (not sure you can do that with containers).
For example I have a profile whose network connections are such that traffic is forwarded through a socks proxy (implemented via ssh). That's basically an ultra-simple vpn. I can then (via a script) automatically launch the tunnel open firefox with the appropriate profile and then exit firefox and gracefully stopping my tunnel.
Mozilla even has two official extensions, trying to explore the space of ease of use/user expectations. In addition to the main multi-container extension they offer Facebook Container which is an extension designed to be more entry level but for folks worried about privacy. (It does what it says on a tin, creates only one additional container, names it Facebook, and automatically moves all Facebook tabs and pretty much only Facebook tabs into it.)