I can make HTML-Markup-Error finding in Mozilla Firefox more comfortable :)
I help you jumping right to the errors you need to fix in "Source View" (Ctrl+U)!

Be aware to choose the bookmark type you want, a static one or an automatically updating one!
Go to this website and drag the bookmarklet into your bookmarklets-list.

Copy bundle.js from dist after building into a console on a Source-View-Page (Ctrl+U) in firefox.

You may also find a way to save a browser snippet in Mozilla, similar to how it's done in Chrome.

To get started, simply run npm run dev.
That will spin up a local server on port 8041.

Open http://localhost:8041 in your browser and drag the provided bookmarklet into your bookmarks bar.

This bookmarklet is automatically reflecting the newest (automatically built) bundle.js-Code in ./dist.

For pushing:
You don't need to build manually; the CI will take care of generating index.html and the bundle.