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-error-message

https://support.mozilla.org/en-US/kb/connection-untrusted-error-message

Websites don't load - troubleshoot and fix error messages

http://kb.mozillazine.org/Error_loading_websites

What do the security warning codes mean

https://www.bing.com/search?q=pr_end_of_file_error

radi.stoyanov said Turns out the option DNS over HTTPS is what caused the problem.

jamesafuf123 said https://support.mozilla.org/en-US/questions/1264659#answer-1237475 my ISP was blocking sites like that

cor-el said This usually means that Firefox wasn't able to find a cipher suites to use to connect to this server and reached the end of the list. There can be two possibilities: one is that the server is outdated and doesn't support modern cipher suites, another might be that the server only supports a few cipher suites and Firefox doesn't support any of these.

You can check your browser and possibly compare this with the server setup.

• https://www.ssllabs.com/ssltest/viewMyClient.html

You can check the connection settings.

• Options/Preferences -> 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":

• https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can