Needs a few small (mostly nominal) changes, but it's qutie awesome Rated 4 out of 5 stars
Minuses: 1. Formally incompatible with latest Nightly, though you said you targeted for Nightly.
2. Addon's name here and in the AOM are different: the word "with" transformed into "on", so the addon's name in AOM makes no sense.
3. Addon's ID is jid1-5PJYJpAc76PKYw@jetpack - why not make it something like NewTabWithHomepage@amanca.fr? It would be a readable ID then. You'd better do this ASAP, as changing addon's ID will make the existing users to not see new updates. Do that faster, to not affect many people.
Pluses: 1. I used NewTabURL and New Tab Homepage addons and they caused a small bug with other addons that create buttons which open some sites - when clicking such buttons - I got redirected to my homepage, instead of those sites.
p.s.: not needed anymore on latest nighlies, since "New Tab Page" feature landed on m-c.