Just as there is the option "Allow screenshots in private mode", I would like to also have an option to allow Copy in private mode. I just copied something, quit Firefox, only to find out my Clipboard was empty.
I'm sorry, it seems the problem is with Google keyboard: you can paste fine, but this keyboard gives as hint (before you start typing anything) a previous copied info, and also in the history of copied items of the keyboard (if you have it enabled) it doesn't appear. But this behaviour doesn't happen when copying from non private window, so there is an improvement to make.
We use the incognito/private mode if the keyboard supports it. I get the same behavior in Chrome in incognito mode. The thing Focus is missing is Fill link from clipboard.