Hi, what security software are you using please ? What error messages if any are you getting please ?

Please try in : SAFE MODE

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

In Firefox Safe mode these changes are effective:

• all extensions are disabled (about:addons)
• default theme is used (no persona)
• userChrome.css and userContent.css are ignored (chrome folder)
• default toolbar layout is used (file: localstore-safe.rdf)
• Javascript JIT compilers are disabled (prefs: javascript.options.*jit)
• hardware acceleration is disabled (Options > Advanced > General)
• plugins are not affected
• preferences are not affected

TEST''''is issue still there ?

Maybe it's this hot issue from last month:

If you get "Secure Connection Failed" and you use either Avast or AVG security software, please see the following article and relevant section:

https://support.mozilla.org/kb/secure-connection-failed-error-message#w_avast-and-avg-security-products