I would say most people aren't coming to Apple looking for the answer,
it isn't necessarily a Mac issue- but being Mac users, with out much help on the internet, we have come here...
It has been an issue in my area (another factor more then likely), being Colorado, for at least a year.
Most people probably, and as I have, just ignore the xfinitywifi log in pop up window by turning it off and then clicking whatever WiFi they're computer should have automatically synced to in the first place.
I have been doing this the whole time over the past year+, and like these people have finally grown sick of Xfinity automatically attempting to take over our WiFi Internet Service no matter where we are. I deleted it as a past network & that did not work. I am guessing perhaps that these other people may be in Denver or Colorado in general or another area where they have this implemented, so probably people outside of whatever areas it is in, this is not happening & people don't know what we are talking about-
It is an automatic pop up window whenever you attempt to get on line, that automatically tries to log you into their network every time you go online, it is beyond annoying. It doesn't matter if you are anywhere you have been or in your own home, their automatic request to join their network doesn't allow your computer to just log into known/saved networks (even with passwords saved)...
Mac users have come here looking to get rid of it because I have googled 3 different searches at least & can't find anything, but here, and some others that were no help to any avail. This may be only happening in this area & it has taken me a year of being annoyed to try to finally get rid of their lame over-riding technology that automatically tries to connect me to their network... this is why there may not be many queries to our issue.
So if there are Mac Users that live in Colorado or elsewhere where Comcast/Infinity has this program implemented (that knows what we are talking about), Please help & save us from this annoying infinity pop up window... Please do share with us how to block InfinityWiFi autologin.
***I am so fed up, I will subject myself to calling the company & be on hold for the next hour probably to find out how to block/disengage their technology, I promise to respond w/ the answer (if they give me one- I'm sure they love the free advertisement flashed every time I go on line but they fail to realize it has only made me hate the Company taking over my computer any time I try to go online via WiFi).