New Tab от Leigh Brenecki

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

The behaviour 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.

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, file an issue.