To correct the problem I have to close firefox and reopen.

This should not occur.

Private windows accept cookies for the duration of your private session.

Are you using automatic private browsing (all windows private) or a regular session with one or more private windows?

In a regular session, I would suggest closing all private windows to clear the private window shared cookie jar. If you are in automatic private browsing, you might need to quit Firefox to accomplish that. (I don't know whether you can use ordinary methods to clear cookies in a fully private session.)

When I search for that particular error code, I can't find it. I can find documentation on many other error messages, but I'm not sure if any of these are applicable:

• "Sorry, but we're having trouble signing you in" error when a user tries to sign in to Office 365, Azure, or Intune - 8004786C, 80041034, 80041317, 80043431, 80048163, 80045C06, 8004789A

• You can't sign in to Office 365, Azure, or Intune

I am using the automatic private browsing (configured from starting up firefox to be in Privatemode). I tried it with only one tab same results. I cannot log back in to the Office 365 email.

I confirmed the error is " error: 800478A1"

This problem means that their is some information being stored in Firefox 45 that I cannot clear hence the only way to recover is to close and reopen Firefox.

When I search that error, there is a lot of jargon about different kinds of Single Sign-on and I can't really follow it... There was a tip on Microsoft's forum about possible workarounds:

Please try again in a few minutes. If this doesn't work, you might want to contact your admin and report the following error: 800478A1.

This is on https://login.microsoftonline.com/login.srf

If I clear the cookie 'PPRelayState' and try again it works fine!
additionally,
If I simply take the 'login.srf' off the end of the Url then it logs me in fine with an SP initiated login.

Source: https://community.office365.com/en-us/f/148/t/354894

Does changing the URL work for you?

If you want to try clearing that cookie on microsoftonline.com, while viewing a page on the site, try either:

• right-click/Ctrl+click a blank area of the page and choose View Page Info > Security > "View Cookies"
• (menu bar) Tools > Page Info > Security > "View Cookies"
• click the padlock or globe icon in the address bar, then the ">" button, then More Information, and finally the "View Cookies" button

In the dialog that opens, microsoftonline.com should be autofilled at the top allowing you to remove the site's cookies individually. At least in a normal window you can, I'm not sure about a private window.

Does it work???

I have tried clearing the cookies but there are none as I am in private mode.

I cannot try a different URL as their is only one to access 365 Email.

I have tried clearing all clearable items such as "clear cached web content", "offline web content and user data" in Firefox with no resolution. the only way to correct the operation is to close and re-open Firefox.

This means Firefox is maintaining information which cannot be cleared.

Hello macre2,

Sorry to hear you're having trouble with Firefox!

Microsoft has a Knowledge Base article on this error and provides a solution. You can read the article here.

Hope this helps! :)

Best, Josh.

Hello macre2,

Sorry to hear you're having trouble with Firefox!

Microsoft has a Knowledge Base article on this error and provides a solution. You can read the article here.

Hope this helps! :)

Best, Josh.

mace2 said

I have tried clearing the cookies but there are none as I am in private mode.
...
This means Firefox is maintaining information which cannot be cleared.

As I mentioned before, private browsing uses a temporary cookie jar shared among your private windows for the duration of your session. I don't think Firefox displays that set of cookies in the cookie dialog, which makes them difficult to inspect and clear. Maybe there is an add-on for managing them but I'm not aware of one.

I have reported this through the Feedback in firefox as this is a problem. If there is a temp cookie jar which cannot be deleted this leaves Firefox open to websites that can insert this information into Firefox and not get it cleared until the Firefox is closed and reopened.

The separate temporary cookie jar that is used in Private Browsing mode tabs is cleared automatically only when all Private Browsing mode tabs and windows are closed (all cookies are session cookies as well). They won't survive a browser restart, but are still there if you close a Private Browsing mode tab during the current Private Browsing mode session.