Vertical/Grouped tabs would be major. All I want after that is a way to switch profiles from the browser like literally any other browser does.
Containers do one thing very well and are very useful, but they don't let you have different bookmarks, add-ons, themes, settings, sync, etc.
A more classic-style profile switcher is available via the '-P' (or '-ProfileManager') command-line switch. If FF is in your $PATH you can run:
firefox -P
The '-P' switch can also take an argument of a profile name to open it directly.But yes, it would be nice if at least one of these options were exposed in the UI so it was more discoverable by users.
There's no way around this. Profile support on Firefox is bad and it's a shame because they've had them for years.