Hi there! I'm sorry to hear you're experiencing issues with updating Firefox. The error message you're seeing, MOZILLA_PKIX_ERROR_KEY_PINNING_FAILURE, indicates a problem with the security certificate on the website you're trying to access. To resolve this, try the following steps: First, check your computer's date and time settings to ensure they're accurate. If they're correct, try clearing your browser's cache and cookies. If the issue persists, temporarily disable any security software that might be interfering with the connection. If you still encounter the problem, it's possible that the website itself is experiencing certificate issues, and you may want to try accessing it later. I hope this helps you get your update done smoothly! If you need further assistance, feel free to reach out to our support community for more help.

Check out this : https://support.mozilla.org/en-US/questions/1146492

I checked the date and time (displayed lower right corner of screen) - same as my wrist watch. Searched for how to clear Browser's cache, found clearing history and cleared everything but site settings. This included clearing cookies. I have to admit I don't know how to turn off my security program and have until the end of the year on my subscription. Firefox still fails to update or download. I opened your second E-mail and some of what was covered was above my pay grade. I don't know what a cer8.db file is or where to look for it or how to do a SSL check. But these did no good for solving the (his)problem. I have Kaspersky, updated minutes before I ask for the Firefox update. My source (Mozilla) should be impeccable not like the POI the other fella was visiting. I am not sure what was happening with the about:support, close, delete Firefox then restart Firefox when I can not download it to update. I went into Kaspersky and disabled the "Encrypted connection scanning", required a restart, and restarted my computer. This did not help so I put things back the way they were. Closed Firefox and restarted in safe mode. No help. I looked at the Public-Key-Pins page, HSTS supported HPKP dropped between 75.0 and 78.0.1. I'm at 115.0.2 looking for 115.0.3! I went to Help> more troubleshooting but found nothing about a profile and did not find SiteSecurity to remove it. I guess I will wait and see if the Key Pin gets fixed. Thanks for trying to help me.