I had the same problem (twice now). After enduring 45 minutes on the phone with their level 1 and level 2 "support", they ended up "re-provisioning" my modem, which I think was essentially rebooting it. After that the login page came up fine. But again, this is the second time it has happened to me, and although they assure me they fixed it "permanently" this time, we'll see happens the next time I log in to pay my bill.
You would think they would ensure access so that I can at least pay my bill.
I have the same problem! It doesn't matter what web browser, any attempt to log in to my Xfinity account on a desktop browser fails with something like:
> Firefox can’t establish a connection to the server at oauth.xfinity.com.
I had to tether to my phone's connection to get connected just to post this response!
This looks like a router DNS configuration issue within the Comcast network. To get into my xfinity account I disconnect from comcast internet and connect through my TMobile internet account through my cell phone - can connect to accout from an outside network! This seemed to have happend when comcast implemented mult-factor authentication and they were never able to get this fixed! It's still an issue....
For some reason, every time I try to login to my account via my home network, the page times out. I have to disconnect from WiFi on my phone in order to login.