I edited the original post because I have realized that the issue is not as I thought in the first place. Instead, apparently there is some issue with persistence in the authorization process with Firebase only in mobile device (it happens the same in my phone and tablet).
In a desktop everything is fine. I have to select the account the first time when I open the browser and after that, no matter if I visit other website, when I come back I just go in the app. But in a mobile device it asks me for the account every time. Considering that I go to a different page with every document visited from the collection, it is quite annoying.
How could I fix that?