You can hide suggested or enhanced sites by clicking on the gear icon on the top right corner of the new tab page, and selecting Classic to show only unenhanced History sites or Blank mode, which turns the sites off.

You can disable suggested sites by clicking the gear icon on the top right corner of the new tab page, and removing the checkmark next to Include suggested sites.

Prevent others from unhiding sites on the New Tab page

You can also turn this feature off completely if you want to prevent others from unhiding your Tiles:

1. Type about:config in the address bar and press EnterReturn.
   A warning page may appear. Click Accept the Risk and Continue to go to the about:config page.
2. Type browser.newtab.url in the search box.
3. Double-click the browser.newtab.url preference and change the url from about:newtab to about:blank. Alternately, you can change it to about:home for your preferred home page by typing in its url.
4. Click OK and close the about:config tab.