It is Comcast's problem, they don't test it in Firefox before releasing the changes and then take many months to fix it. Using IE switch to the Xfinity Connect Lite preference. Then open it in Firefox.

Going to Xfinity Connect Lite does not work for me. Once upon a time the URL Xfinityconnect.mail.comcast.net worked, but no longer.

Since they are partially owned by Microsoft they know what poor public service is. What is the next suggestion on getting back to reasonable operability? I have a new spelling and grammar checker running in the background. Could any of those services or the multiplicity of add-ons be affecting my computer's performance. I have tried starting my computer with Firefox but without add-ons.

An internal link like that hasn't worked for me for a few years now with Comcast. Every one I have used in the past has been given a re-direct to the main Comcast page - http://xfinity.comcast.net/ . IMO, Comcast wants all users to go thru that "portal" page.