Both these references to an “external JS file” are only there so a user can copy and paste the embed code for a quoteback (just like a tweet embed). Here’s line 157 from newcontent.js:
It’s only used to copy the file (as a text string) so the user can embed on their site.
The same file is in fact contained in the extension - this is the version we use inside the extension. But we need to provide it to the user via a CDN link for the embed