Try reducing the zoom level on the page. For example, hold down the Ctrl key and press the - key once or twice. This will shrink the thumbnail images. But it also will shrink the text.

If you can't find a zoom level that works well, you could try an add-on such as the following:

https://addons.mozilla.org/firefox/addon/new-tab-tools/

Click the small wheel/gear/cog icon at the upper right of the new tab page to adjust the display from the initial 3x3 to your preference. (I didn't see a way to keep a search box in the page, however.)

Also, your Firefox identified itself to the forum as version 43. An update is available: this article describes how to get Firefox 49.0.1 using the "About Firefox" dialog on the help menu: Update Firefox to the latest release.

If something is holding you back from upgrading to Firefox 49, please let us know so we can suggest solutions or workarounds. Version 43 is not secure; Mozilla discloses security flaws after each new release.

Sometimes Firefox reports the wrong version because that information was saved in a preferences file. If the "About Firefox" dialog (see first article link) shows Firefox 49.0.1, you may need to clear out that incorrect information. See: How to reset the default user agent on Firefox.