Fóram Tacaíochta Firefox

For the last two months I am unable to use a Classmates.com webpage that I have been using for 15 years. It suddenly keeps giving me the following error message Secure Connection Failed

An error occurred during a connection to www.classcreator.com. PR_CONNECT_RESET_ERROR

Error code: PR_CONNECT_RESET_ERROR

   The page you are trying to view cannot be shown because the authenticity of the received data could not be verified.
   Please contact the website owners to inform them of this problem.

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I have contacted the company and they keep telling me it's my connection or browser and they can't help me. I know there is probably one setting that somehow is wrong but I can't get anyone to figure it out for me. I have tried everything possible. Can this be a browser setting that will not let me edit anything on this webpage? I can edit on other pages that are basically the same type of program ( reunions for schools) PLEASE HELP. YES, MY SECURITY CERTIFICATE IS PAID UP AND ACTIVE.

I can't get Firefox to store bookmarks on my Mac since I installed Monterey 12.0.1. I managed to find some instructions on your trouble shooting page but they do NOT work. Hate to give you guys up, but unless y'all can help me fix this, I'll be moving on.