Help us help you by providing evidence of the issue. What site? Do we need to login to see the issue? Did you try with Firefox in Safe Mode? https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode

Thanks for your reply. The website is walgreens.com. The problem occurs after entering my user name and password and click the "login" button. I do not get logged in but a message appears saying that the site is unavailable and to try again. I have rebooted and that did not resolve it. I started Firefox in safe mode and the error still occurs. I have cleared the cache and I have renamed the preferences file (prefs.js) and that did not resolve it. There are no prefs.js.moztmp or user.js files. Thanks for the help.