Have you tried clearing cache and cookies then?

May you please try the instructions in the Websites say cookies are blocked - Unblock them article.

Thanks in advance!

You can also try if it works in a Private Browsing mode window.

If clearing cookies doesn't work then it is possible that the cookies.sqlite file that stores the cookies is corrupted.

Rename (or delete) cookies.sqlite (cookies.sqlite.old) and delete other present cookie files like cookies.sqlite-journal in the Firefox profile folder in case the file cookies.sqlite got corrupted.

• http://kb.mozillazine.org/Cookies
• https://support.mozilla.org/kb/Deleting+cookies