On: Firefox 81.0

[mkskm]

This is fixed now with the Limit to Designated Sites feature. It's a little buried though: click the multi-account containers button in the title bar > the arrow next to your Google container > Manage This Container > Limit to Designated Sites.

[thrwn_frthr_awy → mkskm]

Thank you. This is the what I am after. Unfortunately Limit to Designated Sites does not work when combined with the Containerize add-on.