I have this issue as well. A new HP laptop, Windows 7 64-bit runnng latest Firefox. My husband runs the same with no problems; he says he's NEVER had this problem in his setup. Bizarre stuff.
Check to see which version of XfinityConnect you are using. To do: From the Preview window in XC, click on Preferences, General. A window opens showing you the two versions...Full and Lite. Which one is checked please? If it is the Full version, switch to the Lite version by checking that version. Close XC, then re-open it and you should be in Lite. Can you access your email nwnow in the Inbox?
Need Email Help? Please post the following information in your post. Do you use XfinityConnect? The Full or Lite version? Do you use an email client? Which one? (Eg; Windows Live mail, Outlook, a smartphone etc.) Which browser/version do you use? And- have you cleared your browser cache? Which operating system? XP, Vista, Windows 7, Mac OS X Details of the problem you are having.