hi nikolaosaek, unfortunately that will be caused by a fault in kaspersky security software on your device which meddles with your connections. the issue should be fixed by kaspersky already when you update its software to the latest version/signature. in case this didn't work, please proceed like this: *go to kaspersky ''Settings > Additional > Network > Traffic Processing'' and uncheck the "Inject script" setting. *in addition, disable the scanning of secure connections like it's described at https://support.mozilla.org/en-US/kb/troubleshoot-SEC_ERROR_UNKNOWN_ISSUER#w_kaspersky and reboot your system afterwards. https://forum.kaspersky.com/index.php?showtopic=351027

Thank you my friend.