You can check the value of the <b>browser.newtab.url</b> pref on the on the <b>about:config</b> page. This pref sets what page opens if you open a new tab with the plus button on the Tab bar or the Ctrl+T keyboard shortcut. See this article about the New Tab page (about:newtab): *https://support.mozilla.org/kb/new-tab-page-show-hide-and-customize-top-sites Your System Details list shows that you have a user.js file in the profile folder to initialize prefs each time Firefox starts. The user.js file is only present if you or other software has created this file and normally it wouldn't be there. You can check its content with a plain text editor (right-click: "Open with"; do not double-click). The user.js file is read each time Firefox is started and initializes preferences to the value specified in this file, so preferences set via user.js can only be changed temporarily for the current session. You can delete the user.js file if you didn't create this file yourself. You can use this button to go to the currently used Firefox profile folder: *Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder) See also: *http://kb.mozillazine.org/Preferences_not_saved

Problem solved. I was putting browser.newtab.url in the wrong place. Thanks to all who answered! B