How to Remove a Digital Certificate
Click “Tools" and select "Internet Options" from the drop-down menu.
Click the “Content” tab in the pop-up window, and then click the “Certificates” button. The window will show multiple tabs for different types of certificates. Browse through the tabs until you find the certificate type you're suspicious of.
Click the three lines icon in the upper right corner of the browser window, and then select “Settings” in the drop-down menu. A new browser tab will open. Scroll to the bottom and click the "Advanced Settings" link.
Look for the HTTPS/SSL entry
near the bottom, and click the “Manage certificates. ” button. A pop-up window will open with multiple tabs. Scroll through the tabs until you find the certificate you don't trust.
Open the browser control menu by clicking the "Firefox" button in the upper left corner of the application window. Select "Options." A pop-up window will open.
Click the “Advanced” icon in the pop-up window, and then click the "Encryption" tab.
Click the "View Certificates" button, which will display the categories of certificates Firefox is using as tabs. Cycle through the tabs until you find the certificate you want to remove.Source: yourbusiness.azcentral.com