Did Not Connect: Potential Security Issue
Firefox detected a potential security threat and did not continue to www.youtube.com because this website requires a secure connection.
What can you do about it?
www.youtube.com has a security policy called HTTP Strict Transport Security (HSTS), which means that Firefox can only connect to it securely. You can’t add an exception to visit this site.
The issue is most likely with the website, and there is nothing you can do to resolve it.
If you are on a corporate network or using anti-virus software, you can reach out to the support teams for assistance. You can also notify the website’s administrator about the problem.
Alla svar (2)
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
You can check the connection settings.
- Settings -> General -> Network: Connection -> Settings
If you do not need to use a proxy to connect to internet then try to select "No Proxy" if "Use the system proxy settings" or one of the others do not work properly.
See "Firefox connection settings":