Firefox tab management is lackluster compared to Chrome; container tabs won't change that :/
Every time I try using Firefox I pretty quickly hit the limitation on selecting tabs. Chrome lets you select tabs like files in a file manager: Shift click for ranges, ctrl+click for adding/removing single tabs. You can then drag & drop the group in or out of various windows, close all at once, etc.
Container tabs imho won't be usable unless something like this is in place. When dealing with as few as 5+ tabs, I certainly wouldn't want to manually tweak them one at a time. Can't imagine for 20+, 50+.
But the idea is nice for feature separation, I like that a lot.