Hi eladopoulos, Please see if @FredMcD's response in this thread can help:

PR_CONNECT_RESET_ERROR https://support.mozilla.org/si/questions/1280856

There is no problem with my antivirus. I disabled it and still problem exists. The problem is with the last edition 74.0 which I suppose doesn't support all the security protocols any more and also might made some other changes regarding security. So, technical team of Firefox could check it and fix it with the forthcoming release.

Hi eladopoulos:

Please post a link to one or more public websites where you see the problem so we can help you further by trying to reproduce the problem.

Cheers!

...Roland

eladopoulos said

There is no problem with my antivirus.

Bing search https://www.bing.com/search?q=PR_CONNECT_RESET_ERROR This simply means, that the peer or some middlebox in between (firewall) is terminating the connection.

Anti-virus is only one of many "middlebox" culprits which generate the error.

The links in @FredMcD's response covers the other ones.

Secure Connection Failed

An error occurred during a connection to www.blogger.com. PR_END_OF_FILE_ERROR

   The page you are trying to view cannot be shown because the authenticity of the received data could not be verified.
   Please contact the website owners to inform them of this problem.

Learn more…

Suffering this problem too, trying to connect to local NAS drive - build prior to 78 allowed me in under 'advanced' options - not available any more sadly