New Tab (shows your homepage) от Andrej Borisenko

This add-on shows your homepage on new tabs, instead of the default Firefox start page.

The behavior of the URL bar is the same as the Firefox start page: it'll be blank and focused, until you navigate away from your home page.

Also this extension respects dark theme to avoid flash of white page when new tab is loading.

This add-on is open source (MPL), and comprises of only about 20 lines of JS. You can read the full source on GitHub, and if something doesn't quite work, make a PR or file an issue.