So just for fun, I went to the Comcast site with Chrome on my Mac. It also worked fine. So, since I was there, I checked on “change my speed”, just for fun, expecting no good offers. Instead, they offered me, a 24 year customer, the 1GB $50/month for five years with no contract plan!
I grabbed it quickly, and finished the sign-up. My modem rebooted, and speedtest now shows my speed at 1195/44.
Thanks for making me look, @edwardp ! 😉