The most excellent LizL., has delivered unto us:

I found out how to install the certificate into the trusted root store:

The certificate has to be saved first and you do that by going to the website and clicking on the Certificate Error and then view certificate. Once you have that opened click on the Details tab. Choose Copy to File which opens the Export Wizard. Click Next at the first screen, choose the correct format and click Next, choose the Browse button and save the file to the desktop with the company name.cer, click Save, Next and then Finish. You should see an widow pop up that says the export was successful.

Once the certificate has been saved open up a command prompt with elevated privelidges, type in certmgr and hit enter. Once open expand the Trusted Root Certification Authorities and then click on certificates. Check for the name of the cert that you want to install and if not there right click on certificates and choose All Tasks then Import. That opens up the Import Wizard. Click Next, click Browse and go to the location of the certificate and click Open. Click Next, choose to place it in the Trusted Root Certification Authorities store and click Next. You will see the settings and click Finish. There will be a popup that says the import was successful. Go to the website and you should no longer have the error.