That worked fine in Firefox immediately after Comcast did the update from Zimbra to Xfinity Connect for their web mail interface, then 3 months later Comcast broke the functionality in Firefox. The Connect Lite interface still works fine for Firefox. Using IE, once you're in the full email page open Preferences -> General in the Xfinity menu header and select Xfinity Connect Lite. Then try it in Firefox. Or, bypass using the View Entire Inbox and click on the first email which is showing on the unread email listing under Compose New. Once you're viewing that email the Folders menu will appear in the left column.