Just like previous versions of Firefox, Firefox 4 offers a whole lot of different ways to customize the default search engine and keyword search criteria, but sadly there is no direct way to tailor the tab opening behavior for viewing search results. For instance, you always get to see the search results in the currently opened tab where search keywords are entered. This can be quite frustrating in situations where you are reading an important article and want to quickly search for one specific keyword, as you need to open a new tab and then use the search bar present at top-right corner. Tab Search is here to change this behavior. It is a small extension for Firefox with one aim; open search results in a new tab.
It doesn’t add a new search bar nor it requires you to configure any settings. Just install the add-in, enter search keywords in search bar, and use Ctrl + Enter hotkey combination to open search results in a new tab.
It is to be noted here that it doesn’t replace default search behavior. You can always use Enter key to open the search results in currently opened tab.
Install Tab Search extension for Firefox 4 (Removed from Mozilla Add-Ons section by developer)