T-Mobile Website Is Not Working On Firefox With Latest Update

This problem is NOT solved.  Since updating Firefox to the latest version about 3 days ago...now cannot log into the T-Mobile site.  Some type of problem with a revoked security certificate. 

I see this issue is marked resolved but I thought my own experience with something similar might help another user. On one phone my daughter was using suddenly there were places that came up blank and particularly you tube for kids.  I would reformat the phone and it would work for a day or two then suddenly back to randomly getting blank pages.  I  actually upgraded the phone and sure enough,after a couple days passed it to was affected by blank pages and videos. Tech support couldn't find any reason for the issue. I figured it out on my own. Here's what solved the issue (been months now). This line was under parental control to prevent them from downloading stuff that would add to the phone bill. (I have kids and grandkids setup this way). I had to change the age of appropriate material for this one line to a higher age and instantly it started working like it should have and has never gave that line any more problems. 

Hope this helps 

DaFattMann 

Yes, it is 121.0 (64-bit) version. There has to be a setting that T-Mobile may require for Firefox to work on their Website. Recently, another Website had similar problem and I contacted the technicians. They were aware of Firefox issues and a week later while still using the same version on Firefox, they resolved it on their own.

Same here.

Is your version of Firefox up to date?  I didn't have any issues logging into my account using Firefox before posting.  I normally use Edge though for the sake of compatibility for banking and account logins.