Hello, PR_CONNECT_RESET_ERROR means that somewhere between you and my.t-mobile.com sent res (reset) packets to you, effectively canceling your tcp connection. The error text you sent is a security feature, in case the computer that sent the reset packets is attempting a MITM (Man in the Middle) attack, so Firefox is refusing to show the information, as it could be a trick.

Web search https://www.bing.com/search?q=PR_CONNECT_RESET_ERROR ''This simply means, that the peer or some middlebox in between (firewall) is terminating the connection.'' There is security software like Avast, Kaspersky, BitDefender and ESET that intercept secure connection certificates and send their own. https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can https://support.mozilla.org/en-US/kb/firefox-and-other-browsers-cant-load-websites https://support.mozilla.org/en-US/kb/secure-connection-failed-firefox-did-not-connect https://support.mozilla.org/en-US/kb/websites-dont-load-troubleshoot-and-fix-errors [https://support.mozilla.org/en-US/kb/what-does-your-connection-is-not-secure-mean What do the security warning codes mean]