New Tab Override (browser.newtab.url replacement) https://addons.mozilla.org/en-US/firefox/addon/new-tab-override/

With Firefox 41 (and higher), it's no longer possible to customize the page shown in a new tab via changing the preference browser.newtab.url in about.config. Because of the fact that hijackers abused the preference in the past, Mozilla decided to remove it (see bug 1118285). Fortunately, by removing it, Mozilla also introduced a new API to bring this functionality back to life as an add-on. This add-on allows the user to choose a certain page in a new tab.

That is a bad decision. Almost every other browser has a way to set this, without adding in an ADD ON. Might see if I can go back to 40 and stop getting updates.

Note that it is possible to do this without an extension via code in the mozilla.cfg file in the Firefox program folder. You can modify the newTabURL = "about:blank"; line to set a different new tab page.

//
var {classes:Cc,interfaces:Ci,utils:Cu} = Components;
var newTabURL = "about:blank";
Cu.import("resource:///modules/NewTabURL.jsm");
NewTabURL.override(newTabURL);
// copy the New Tab URL to browser.newtab.url for convenient checking the setting in about:config
pref("browser.newtab.url",NewTabURL.get());

You can use a mozilla.cfg file in the Firefox program folder to lock prefs or specify new (default) values.

Place a local-settings.js file in the defaults\pref folder where also the channel-prefs.js file is located to specify using mozilla.cfg.

pref("general.config.filename", "mozilla.cfg");
pref("general.config.obscure_value", 0);

See Configuration:

• https://developer.mozilla.org/en-US/Firefox/Enterprise_deployment