[SOLVED] SEC_ERROR_BAD_SIGNATURE in Mozilla Firefox internet browser!

If you are getting the "SEC_ERROR_BAD_SIGNATURE" error on latest Firefox version 89.0.1, then the solution is: 1. From the "Three Horizontal Lines" button at top-right, select "Settings". 2. Clear your History (everything). This step may NOT be necessary. 3. Go to "View Certificates". 4. Select the "Authorities" tab. 5. Locate the concerned Certificate, they are listed in alphabetical order. 6. Click on "Edit Trust". 7. Select both options "This certificate can identify websites" and "This certificate can identify mail users". NOTE: The first time you do this and visit your site, Firefox - like any other browser - will warn you "Potential Security Risk Ahead". Since, IF, you trust this site - click "Advanced" and accept.