After signing into xfinity (comcast) you can select to go to their mail via connect.xfinity.com which takes you to their email web app. It was working fine with the previous version of Firefox, been using it for years. It will load other emails, such as secondary email, but my primary personal email throws an error, unable to connect to server try again later. I contacted Xfinity support and they asked me to try another browser. I tried under Google Chrome and it works.