It is not possible to use the Primary Password.
In version 146.0.1, or perhaps even earlier, I noticed that if you set a Primary Password to log in to the browser, you can reset it and log in simply by clicking the "Cancel" button. This allows you to access all of your user tabs and links. I hadn't noticed this before. It defeats the purpose of setting a Primary Password. I noticed similar issues in the Tor browser, but you can't set a Primary Password there at all, even though the feature is there, and it's built on the Fire Fox engine. Please fix this issue. No buttons should allow you to log in without entering the correct Primary Password.