Install a PK12 client certificate from a URL?

I need my add-on to detect a mime type of application/x-pkcs12 when the accesses a file via URL/HTTP and then save it to the certificate store for Client Certificates (used to identify the browser to the server).

I know JavaScript well, but it’s been a while since I’ve done extensions and now there’s this new “WebExtension” API that we’re all supposed to use.

I think I should be able to use a webRequest event and check the webRequest.ResourceType to get the download, but I’m not sure what function inserts a certificate to the store. Any thoughts?

Can use the ResourceType field to get this kind of information? https://developer.mozilla.org/en-US/Add-ons/WebExtensions/API/webRequest/ResourceType