1. Open Firefox and click on the three lines in the top left corner of the main window.
  2. Type “firefox://search” into the address bar and hit enter.
  3. A list of search results will appear, with a link to the search you just performed.

 

New Search Tab with Hotkey

Just search using Alt+Enter instead of hitting the normal Enter key. This will work even if the default is still the current tab.

 

New Search Tab by Default

Type about:config into the address bar, and then put the following into the filter box:

Double-click the value to change it to true.

 

New Search Tab with Tab Mix Plus Installed

Open Tab Mix Plus Options through the Tools menu. Click on Events.

Check the box for “Search bar” under the “Open tabs from” section.

New Search Tab with Middle-Click

You can also middle click the search button after entering text into the search box. (Thanks to markdr in the Lifehacker comments for this one)