FIXED – You can’t get there from here
With Office 365 Conditional Access Policy security applied users will see the error below when attempting to view SharePoint Online with a different browser (FireFox, Chrome, etc.). This makes debugging front end JavaScript applications challenging without Chrome’s excellent F12 debug tools.
However, we have a fix.
Leverage Internet Explorer to obtain a valid Office 365 session and export those cookies to text. Demo video shows exactly how to extract the “FedAuth” and “rtFa” cookies to successfully login from any web client (FireFox, Chrome, Fiddler, REST Post Man).
Cheers!