installing a certificate on thunderbird

I receive an email from comodo and click on the tag to install my certificate. But how do I know my certificate is installed. When I look for it there is nothing there. The information for thunderbird must be outdated or something because my pop pages do not match their instructions. I was able to find (I think) where to import but I don’t know what PKCS12 is and where to find it. Can anyone help.