Jive Search - A search engine that doesn't track you.
Trufflepiggy - Quick Search - The all-in-one search addon: just select and search. Find on multiple websites at once. Search via overlay, context menu or omnibar. Featuring anonymous profiles. Easy setup: select from 1000+ user generated searches. Cross-browser sync.
Yase - Yase is a privacy friendly search engine
ContextSearch web-ext - Search for selection with your browser's search engines via a pop-up.
DuckDuckGo - The Internet privacy company that empowers you to seamlessly take control of your personal information online, without any tradeoffs.
Selection Search - With this extension you can easily search for text you have selected.