Only use the browser that ask you again for exten/password. That means that the browser is connecting to the fop2 server and it is getting an incorrect login response from the fop2 server. That is good.
Using that browser then, enter a correct extension and password. What is correct? Depends on your fop2 configuration, something you did not give information about. If you use the stock configuration, in a freepbx system, and if you installed fop2admin for freepbx, a correct extension/password is set in the "fop2 users" menu in freepbx. In this case also, you can see a list of valid exten/passwords by running, in the command line:
/usr/local/fop2/autoconfig-users-freepbx.sh
Best regards,
