I was also having issue when I paid my bill on the 9th. Just tried with Nightly an it went right in without having to tweak my add-ons. see screenshot Try a different version of Firefox (Beta, Dev, or Nightly) and see how it works. Make sure to install in a different directory than your current install.

"waiting for bat.bing.com"(a tracking cookie)error that can be seen in bottom, left hand corner.

Try turning off or tweaking ETP.

I was also having issue when I paid my bill on the 9th. Just tried with Nightly an it went right in without having to tweak my add-ons. see screenshot Try a different version of Firefox (Beta, Dev, or Nightly) and see how it works. Make sure to install in a different directory than your current install.

I'm not going through the hassle of installing a different version and having to set everything up all over again. I'll just have to switch over to Duckduckgo if Mozilla doesn't get involved and explain how to actually fix it.

simpleman2 said

"waiting for bat.bing.com"(a tracking cookie)error that can be seen in bottom, left hand corner.

Try turning off or tweaking ETP.

What is ETP? Your not showing how to pull up the options in your print screens. How do I pull up "Protections for login.xfinity.com?

ETP is here. see screenshot

I still can't get into billing even after turning off ETP. See attached

Once again I had to use the Duckduckgo browser to pay my Xfinty bill. Since there doesn't seem to be a way to get technical support directly from Mozilla I'm dumping Firefox for Duckduckgo, it's a shame, I've been using Firefox for many years, all the way back to the Waterfox days. This is what happens when a company doesn't provide real tech support.......they loose customers.

Before you go. You can also try Refreshing Firefox. https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings

It's time for me to pay my bill, let me see what happens.

I got in with no issues. see screenshot Any security software besides MS Defender?

Before you go. You can also try Refreshing Firefox. https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings

If I do a refresh I will be losing everything (Profile) and starting over from scratch. I don't want to have to setup everything all over again.

I got in with no issues. see screenshot Any security software besides MS Defender?

Yes, I have Bitdefender Total Security, but it's not preventing me from logging in using any other browser. Before you ask, there is no way to turn it off, only completely uninstall and it's a real pain to reinstall because I'm running a dual boot system. I just tried logging in again....see attached.

I think it has something to do with tracking cookies. When logging in with Duckduckgo I click on Fire and clear Data and this it lets me login. See attached Here is are all the tracking cookies that Duckduckgo clears before letting me login. see attached

Bitdefender Total Security... Just because the software works with other doesn't mean it won't cause an issue in Firefox. If your running Windows pro, try windows Sandbox option to test. https://www.howtogeek.com/399290/how-to-use-windows-10s-new-sandbox-to-safely-test-apps/ If windows home, then you can try windows in Safe Mode with Networking to test. The next step will be to uninstall Bitdefender Total Security. Also, ETP is here. see screenshot

I know for a fact that it's not a Bitdefender issue. Every once in a while it will let me in. I just got in after putting in my password, walking away and coming back 20 minutes later. See attached

It's a cookie/tracker issue, they are not loading correctly, hanging up. That's why I keep see the handshake error in the address bar and Xfinity can continue until they are done doing their thing first.