I'm having the same issue, it's not a local computer issue. I have tried using ie and chrome on two different computers. I have also had someone 15 miles away on a different computer try to get into my email with no success, they were however able to access their own email.
My mobile xfinity doesn't work either. There is apparently nothing we can do to repair the situation on our end. We just have to call the fine folks at comcast and have them tell us that "they have to escalate the problem and call us back in 24-48 hours" Good luck with yours!
having the same problem as of today the 13th of January 2012. Tried calling comcast but the wait time is to long and then they ask that they will email me that's fine But I can't open my email. This problem has to be on there end.