Have you seen?

• https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save#w_user-js-file-overriding-preferences

Also make sure that the New tab page is enabled.
The browser.newtabpage.enabled should be true.

To which page are you trying to change the browser.newtab.url pref?

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

Thanks for trying but New tab page is enabled. This is not all that important. I'm just annoyed that it isn't as easy as it should be. New tabs currently go to Bing (I don't know why) and I want to change them to Google.

Delete the user.js in the profile folder as i stated above.

Also see

• Remove a toolbar that has taken over your Firefox search or home page

As possibly you have something installed that you do not really want. And then use the search reset addon to easily reset preferences.

• https://addons.mozilla.org/en-US/firefox/addon/searchreset/

Note as a power user who is able to use about:config you will probably wish to use the control panel method to remove extensions and NOT the Firefox Reset method

• Read the article before considering using Refresh Firefox - reset add-ons and settings
  (Close unnecessary open tabs, bookmark any remaining ones and home sites of extensions. You will lose some information when resetting )

I did that. Removed the line browser.newtab.url in user.js file and then saved but no difference

user.js

• What other content is in the user.js file
• It may help if you paste the text content of the file into your next message
• Who or what created the file ?
  You manually or some software
• Note the file does not exists by default in a standard Firefox install
  http://kb.mozillazine.org/User.js_file

See also:

• http://kb.mozillazine.org/Preferences_not_saved

The contents of the user.js file are below. I have done nothing myself to customize Firefox other than set a homepage, but have had some unwanted toolbars, etc. arrive without being invited. I'm able to keep the computer clean by being vigorous with my anti-spyware, anti-virus, C Cleaner, etc.

I do some pretty sophisticated things with music production software, but this is not my area.

user_pref("extensions.delta.tlbrSrchUrl", "");
user_pref("extensions.delta.id", "f0eb830c000000000000001fc6d7181f");
user_pref("extensions.delta.appId", "{C26644C4-2A12-4CA6-8F2E-0EDE6CF018F3}");
user_pref("extensions.delta.instlDay", "15788");
user_pref("extensions.delta.vrsn", "1.8.10.0");
user_pref("extensions.delta.vrsni", "1.8.10.0");
user_pref("extensions.delta.vrsnTs", "1.8.10.016:42:32");
user_pref("extensions.delta.prtnrId", "delta");
user_pref("extensions.delta.prdct", "delta");
user_pref("extensions.delta.aflt", "babsst");
user_pref("extensions.delta.smplGrp", "none");
user_pref("extensions.delta.tlbrId", "base");
user_pref("extensions.delta.instlRef", "sst");
user_pref("extensions.delta.dfltLng", "en");
user_pref("extensions.delta.excTlbr", false);
user_pref("extensions.delta.admin", false);
user_pref("extensions.delta.autoRvrt", "false");
user_pref("extensions.delta.rvrt", "false");

Hmmm.... I just registered that all of these files have delta in the name and Delta Toolbar was a very unwelcome, unwanted guest parasite I had some time ago. Should I just delete all of my js?

Hello farmuk, YES delete the file.

Also uninstall Delta or any unknown programs from the control panel.

Thank you everybody for trying to help me. I decided there were too many variables to isolate a particular setting and just reset Firefox which I'm sure somebody did advise me to do. I was trying to avoid that because I was worried that I'd lose passwords, etc.

It all seems to be ok and I've learned a few things, thanks.