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 There can be two possibilities: one is that the server is outdated and doesn't support modern cipher suites, another might be that the server only supports a few cipher suites and Firefox doesn't support any of these.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.

Thank you guys for useful info! The DNS option was in off position all time. Nevertheless, it is not a Firefox browser problem I think. Internet Explorer also cannot read the problematic sites. Antivirus switching off has not bring positive results. But, but... Firefox browser on the other PC with Windows 8 OS has no problem with the sites. So, the most probable source of the error is on servers of problem sites (as jamesafuf123 said) or other ideas are necessary to be found.

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