It could be that the bookmarks toolbar was turned off. Move your mouse to the top of the Firefox window, to an empty area by the tabs. Right click. You should now see a list of toolbars. One is for bookmarks. If it is off, click it to turn it on. If it is on, click it to turn it off, then turn it back on. Sometimes when my FF starts, my bookmark toolbar is there, but with no entries. Turning it off, then on again brings it back.

You can use the SearchReset extension to reset some preferences to the default values.

• https://addons.mozilla.org/firefox/addon/searchreset/

Note that the SearchReset extension only runs once and then uninstalls automatically, so it won't show on the "Firefox > Add-ons" page (about:addons).

You can check the browser.newtab.* pref(s) on the about:config page and reset user set (bold) prefs via the right-click context menu to the default value.

• http://kb.mozillazine.org/about:config

See this article about the New Tab page (about:newtab):

• https://support.mozilla.org/kb/new-tab-page-show-hide-and-customize-top-sites