Hi, what you comment seems to be a privacy and security issue. Try going to "preferences", "privacy and security", and check "Accept cookies and site data from websites (recommended)"

A major difference between a regular window and a private window is that the private window doesn't use the disk cache and use a separate cookie jar, so cookies from a regular window can't be accessed in a PB mode window.

You can check for issues caused by corrupted cookies and clear the cookies for involved websites and clear the disk cache.

Clear the Cache and remove the Cookies for websites that cause problems via the "3-bar" Firefox menu button (Options/Preferences).

"Remove the Cookies" for websites that cause problems:

• Options/Preferences -> Privacy & Security
  Cookies and Site Data -> Manage Data

"Clear the Cache":

• Options/Preferences -> Privacy & Security
  Cookies and Site Data -> Clear Data -> Cached Web Content: Clear

If you use a bookmark to access a specific page then instead navigate to this page starting with the main page or the sign in page in case there is a problem with this bookmark. Best is to avoid creating a bookmark that can possible contain GET data in the link or (hidden) POST data that may no longer be valid.