Glad you like the Add-on and Thanks for reporting your Left Mouse Click Issue. I've checked and this is a regression from an earlier version - this used to work, but it wasn't unfortunately covered with a test. Fixed it and released version 0.84, should now work as expected.

If you enable Multi-Account Containers Isolation you really only can load URLs in Containers if they're assigned. So it might happen that you try to e.g. open "example.com" in a Container, while only "www.example.com" is assigned. I'll try to enhance visibility over what is assigned and a way of adding new MAC assignments directly in the future.

Hope that helps. If something still doesn't work as expected or something else pops up, I'd encourage you to open a new Issue on GitHub: https://github.com/stoically/temporary-containers/issues