Recently multiple desktops of mine have updated to Windows 10 latest Creator's Update. Apparently this involves a significant change to the Edge browser that integrates Flash, but doesn't default enable it. Accordingly, trying to sign-in to Xfinity TV streaming through that browser runs into problems. Per instructions along the way, I enabled Flash for both the website AND in general in Edge.
On two desktops, that resolved the issue. On the third (an off-brand "BeeLink" small footprint computer), nothing seems to work; I have enabled and disabled, attempted to re-download Flash (which I can't because Edge says Flash is integrated), clicked on the symbol to the left of the URL and/or on the Flash icon in the address bar to enable, all that. I've tried everything I can find, multiple times, and still get an error.
Specifically: I can login. I can get to "Adding device..." and it fails with the following message: "Sorry, we're having some trouble... Xfinity stream is not available" and this error code below: "Error ftde.xact.DrmRequest.exists: Exception calling flash method (DrmRequest) (Error)"
Update: I installed Firefox, and get the same error. It appears to me that the login screen uses Flash, since that is where I see my first error if Flash is NOT enabled. Once past the login, and going into "Adding device...", that's where it bombs out. Same exception error in Firefox. The Chrome browser works fine; I can login, adds the device, and goes to the Xfinity streaming page where I can watch live, recordings, on-demand, etc.