Swagger Editor (Local) CORS Error

Sorry, a Noobie question...

Currently developing an OAS against one of our vendor's REST APIs for ingestion into Salesforce.  I've downloaded the latest version, ran the ndm install, fired up the index.html, cleared the editor and began building the spec.  All is going well until I want to test my first path against the vendors root (no authentication) which should just return some HTML but I am getting the following which I see other users experiencing...

The HTTPS URL being built by Swagger Editor is correct...copy/pasted into another tab.  What am I missing or what may I have missed installing the local Swagger Editor?

Again, sorry I'm just a noob and trying to learn this.  This spec would help me immensely if I can get it into my Salesforce Dev Org!

Thanks in advance for the help!   ------Jim