First I was happy, since it seemed to does exactly what was advertised.
Opening a completely new Tab first looks, like its the default container, but switches correctly after entering a search.

Then problems occurred too often to be ignored.
Sometimes it clashes with tabs, that want to be in a concrete container and keeps reopening them to infinity.
Sometimes opening a new tab in a different container results in the extension switching that container back to the last one, even if I wanted that new container.

All in all I am happier with the Simple Tab Groups extension, where I also get my new Tabs correctly contained, while being in the correct group. (Since that extension comes with a lot more functionality, it couldn't be everyone's cup of tea)

I really liked this until I realized that this was causing my firefox new windows to close the second they open. I believe the problem comes from the extension being unable to decide which container to open a new tab in a new window in, so that needs to be changed. I would love to rate it higher, but this is a really bad bug

Didnt work as expected. Inconsistent behaviour. Works intermitently.