Applying the following CSS using Stylish or userChrome.css will style the blank New Tab page appropriately!
background-color: rgb(229, 229, 229) !important;
-moz-linear-gradient(rgba(255, 255, 255, 0.5),
rgba(255, 255, 255, 0.2)) !important;
background-attachment: fixed !important;
Since the default browser background color is white, there may be a momentary flash when you open a new tab. To minimize this effect, you can set the
browser.display.background_color preference in
#eef0ec. Restart Firefox for this change to take effect.
Note: This color was chosen based on averaging the Most Visited page's background to a palette of two colors. Feel free to suggest a color which minimizes the flash even further.