This is exactly what I needed. I was about to switch to Chrome for work purposes when I discovered this. Thank you, thank you!

Anyway, one slightly annoying detail that I'd like to report: On Windows, after pressing Ctrl+T to open a new tab, the URL bar gains focus for a split second but as soon as the container is set it loses it. I wish I could just press Ctrl+T and start typing the URL immediately. Now I have to press Ctrl+T, then press Ctrl+L or F6 and then I can start typing.

Works exactly as expected and very easy to use. Excellently recreates Google Chrome's profile system.

works as expected so far, I really needed something like this

Doesnt work importing Tree Tabs groups (tabs imported unloaded). It changes the container only when tab is clicked/loaded, loses the tab order placing it at the top of the list. (At least the container tabs rightclick method opens it next to the old tab). Might be fixed if old tab is closed AFTER the new tab is opened?

Update: It does work! Just that the new-tab page doesn't reflect that. It shows the container only *when* a URL is loaded. It's not the same as opening a new container tab from the main container extension (that one does show the new-tab page with the container color and name). The user has to take a leap of faith (potentially risky) by loading the URL without receiving adequate affordance (like the color and name) in the new-tab page.
Star increased :)

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Doesn't seem to work for me on MacOS 10.14.4 with Firefox 66.0.3. Created new window, switched container, closed the first non-container tab, then created new tabs with cmd+t but they are regular non-container tabs.