I've been using New Tab Tools for about a year now, but after the Quantum update, I used the legacy version, and as soon as the new update came through, New Tab Tools refused to start. Now, whenever I open a new tab, it tells me that "New Tab Tools couldn't start properly". I've disabled all other Add-Ons, whitelisted it in cookies, set Firefox to Remember All History and made sure my about:config is correct, all to no avail.