DuckDuckGo for Firefox is the search engine that gives you great results and doesn't track you.

It will also provide you with smarter answers and less clutter while in use. This extension makes DuckDuckGo available in the address bar, search bar, and the right-click menu. DuckDuckGo for Firefox also adds a handy toolbar button with more included features!

DuckDuckGo for Firefox will:

Add a handy DuckDuckGo toolbar button to your browser for easy access to !bang tags (removable).
Add DuckDuckGo as your default search engine through the address bar, search bar and context right-click menu (reversible).
Show DuckDuckGo instant answers on Google/Bing (removable).

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