Let's stat with; Some problems occur when your Internet security program was set to trust the previous version of Firefox, but no longer recognizes your updated version as trusted. Now how to fix the problem: To allow Firefox to connect to the Internet again; * Make sure your Internet security software is up-to-date (i.e. you are running the latest version). * Remove Firefox from your program's list of trusted or recognized programs. For detailed instructions, see '''[https://support.mozilla.org/en-US/kb/configure-firewalls-so-firefox-can-access-internet Configure firewalls so that Firefox can access the Internet.]''' {web link}

[https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode Start Firefox using Troubleshoot(Safe) Mode] {web link} A small dialog should appear. Click '''Start In Troubleshoot(Safe) Mode''' (not Refresh). Is the problem still there? 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-firefox-did-not-connect https://support.mozilla.org/en-US/kb/websites-dont-load-troubleshoot-and-fix-errors [https://support.mozilla.org/en-US/kb/what-does-your-connection-is-not-secure-mean What do the security warning codes mean]