Starting with Firefox Quantum (version 57), there is a new user interface (UI) called Photon.
By default, Firefox displays Search bar, Top Sites (sites you visit most), popular articles Recommended by Pocket, Highlights (sites you’ve visited recently or bookmarked), and Snippets (updates from Mozilla) every time you open a new tab.
By default, Firefox only shows one row of Top Sites on the New Tab page. You can change to show as many rows of Top Sites you want on the New Tab page. This will add more sites to the Top Sites section on the New Tab page.
This tutorial will show you how to change the number of rows of Top Sites to show on the New Tab page in Firefox for your account in Windows 7, Windows 8, and Windows 10.