Steps to fix Firefox if it is not secure:

• Firefox's Clear Browsing History-Open Firefox and go to the top-right corner of the browser and click the three lines button. Then select Options -> Privacy & Security from the drop-down menu. Scroll down to History in the right pane and click Clear browsing data. Choose a time range, such as All Time, and check all of the boxes under Browsing history. To remove all browsing history on Fire, click the Clear Now button.
• Date and time should be corrected.-Many websites make use of security certificates, which have an expiration date. If your PC's date and time are incorrect, your browser may detect that the certificate is out of date and display the notice 'Your connection is not safe' in Firefox. You may adjust the date and time by right-clicking the Date and Time symbol in the bottom-right corner of your computer screen and selecting Adjust date/time.
• Check for malware and temporarily disable anti-virus software.-Malware or antivirus software can sometimes interfere with your Internet connection, resulting in the Firefox your connection is not a secure error. Using Windows Defender or third-party security software, run a malware scan to eradicate malware.
• To fix Firefox, restart your router. Your Internet Connection Isn't Safe-Then uncheck the box that says 'Set time automatically.' Turn this option back on after a while. You can also manually alter the time and date by clicking the Change button. To turn off your router and modem, push the power button on the router and modem. To turn on the router/modern, click the power button again after around 1 minute. Then reopen Firefox and visit the target websites to see if the 'Your connection is not secure' issue remains.

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