When I open the email for the daily newspaper and click on "read today's paper," I get the sign-in box. I have added the newspaper to my acceptance and permission sites and how do I fix this?

I receive two daily newspapers. For each, I added the emails to the acceptance list so when I get the email, I open it and click on the box, "read today's email." One works perfectly. The other one doesn't. It was working and with the recent updates, it has stopped working. Every time I click on "read today's paper," I get the sign-in box. Why is this happening and what can I do or Firefox do to correct this problem? I added the paper to the exception box (manage exceptions and cookies) but doesn't seem to make a difference. I have added two different options for the paper, but neither seems to produce the automatic sign-in. I wrote to the tech director of the newspaper several times. The first time she fixed it then an update set me back to square one. The second time she recommended putting the info into the exceptions and cookies. I did and it worked until this most recent update. Now, nothing seems to work and I have stopped the protection guard on the browser window. What are or is a solution? Thank you.