If you are using Firefox and are not able to log in to Marker.io when reporting, you might want to change your privacy settings.
To allow third party authentication, go to Firefox and in Preferences, you need to chose one of the following highlighted options:
Alternatively, if you want a higher level of privacy, you can chose to block All third-party cookies and add Marker.io as an exception by going under Cookies and Site Data and clicking Manage Exceptions.
Then, add marker.io and api.marker.io as exceptions by clicking Allow and finally Save Changes.
That's it! You should now be able to report bugs while being authenticated in Marker.io.