Imagine not having that and for each new window you have to relogin and on some sites it will log you out of the other session. This allows multiple tabs in private mode.
my password manager makes the login process pretty fluid... but either way, incognito is not regular browsing... it is supposed to forget cookies and such tracking mechanism.
I think that Mozilla are trying to make addons disappear.... they started with Firefox Mobile, only about 10-15 addons are available now (which is why I use an ancient version of Firefox Mobile).
They are getting a lot of money from Google, so it MIGHT be a request from Google.
dang, can you fix it?