I got this error sometime today after doing a system upgrade:
Your Computer Clock is Wrong
Your computer thinks it is 6/2/2022, which prevents Firefox from connecting securely. To visit www.youtube.com, update your computer clock in your system settings to the current date, time, and time zone, and then refresh www.youtube.com.
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.
I fixed it by running:
sudo timedatectl set-ntp true