Sometimes I want to do some general browsing within container tabs, and I find it inconvenient that I need to long-hold on the + to get a new tab in the container when I am already in the container. It might be nice to create new tabs in the same container as the currently selected tab when pressing the new tab button or the key-chord C-T

Bug 1245262 should add a keyboard shortcut for the same action to quickly select the container, you can also lower the timer too to something like 300 ms too. I'm not convinced myself that we should auto put the user in the container in the new tab. The reason being is that it is easy to forget you are in a container and open a site that you didn't want knowing you are logged into Facebook for example.

Bulk change per https://bugzilla.mozilla.org/show_bug.cgi?id=1401020

I'm not sure if this has been discussed elsewhere or during the development of containers, but what about tying a container to a window, rather than a tab. Personally, this would be more consistent with how I work and would make the new tab button and menu more clearly associated with a container.