Is the new tab blank or does it show content from a particular site?

Another user had a second tab opening (blank) and it was caused by one of his extensions. Even if you do not recall installing one, they can sneak in when you install other software.

Please check for nonessential or unrecognized extensions on the Add-ons page. Either:

• Ctrl+Shift+a
• orange Firefox button (or Tools menu) > Add-ons

In the left column, click Extensions. Then, if in doubt, disable (or remove).

Usually a link will appear above at least one disabled extension to restart Firefox. You can complete your work on the Add-ons page and click one of the links as the last step.

Does that get rid of the extra tab?

Note: If there is no Remove button, the extension was installed externally to Firefox. You can check the Windows Control Panel, Uninstall a Program. If you click the "Installed on" column heading to sort by date and scroll down to about the time the problem started, you might be able to spot the problem.

This issue can be caused by the MySearchDial extension.

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

You can check if 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) if you didn't create this file yourself.

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.

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

You can use this button to go to the currently used Firefox profile folder:

• Help > Troubleshooting Information > Profile Director: Show Folder (Linux: Open Director; Mac: Show in Finder)