Webextension polyfill add to manifest.json

Hi! I need a bit of help with the polyfill integration…
I added the polyfill via the npm command as per the instructions:
npm install --save-dev webextension-polyfill
But if I simply add the browser-polyfill.js to the manifest.json file (again as per instructions in the github readme) the extension cannot find the file.
If I copy the file from node_modules/webextension-polyfill/dist/browser-polyfill.js to the project root it works.
Do I have to copy the .js file first? Or am I missing something?

Based on your comment I’m guessing that you are not using any bundling tool (e.g. webpack), in that case you can just copy the polyfill source file into your extension source dir (manually, or using a small nodejs script if you prefer) and then use it like you would use any other js file included in the extension (e.g. including it in a manifest property or in an extension html file etc., right before any of the js scripts that are going to use the browser.* API methods).

yes, I’m not using any bundling tools, I added webextension-polyfill to the devDependencies of the extension, then I added a script to copy the file.
It works, but I’m not sure it’s the proper way:

"scripts": {
	"prepare": "cp node_modules/webextension-polyfill/dist/browser-polyfill.min.js ."