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 [https://support.mozilla.org/en-US/kb/websites-dont-load-troubleshoot-and-fix-errors?redirectlocale=en-US&redirectslug=Error+loading+web+sites Websites don't load - troubleshoot and fix error messages] http://kb.mozillazine.org/Error_loading_websites [https://support.mozilla.org/en-US/kb/what-does-your-connection-is-not-secure-mean What do the security warning codes mean] https://support.mozilla.org/en-US/kb/what-does-your-connection-is-not-secure-mean Often, "Secure Connection Failed" means "Connection Failed (trying to load a secure page)". In other words, not a security problem, just a connection problem.

I don't have any anti virus installed on my PC .But Malware bytes installed

Update Malware. If the problem continues, disable it.

''raja19 [[#answer-1214040|said]]'' <blockquote> I don't have any anti virus installed on my PC, but '''''Malware Bytes''''' installed. </blockquote> * If you have the FF '''Malware Bytes''' Extension installed, disable it for now. I have it, but even with its most recent Update, it is still a problem Extension, so again... I have it Disabled for now. Other Items that may help: * I have '''Content Blocking''' set to '''Standard'''. * If you have any Script-Blocking Extensions (Ad-Blocking, etc), check these by doing: '''Menu > Help > Restart With Add-ons Disabled'''. Don't use multiple Extensions of the same type/function. Example: Don't have two or more Ad-Blocking Extensions. Pick and use just one. ~Pj