Context Search - Context Search is a Firefox extension that expands the context menu's 'Search for' item...
Unbubble - THE SEARCH ENGINE FROM EUROPE 100% NEUTRAL, SECURE & CLEAN
Swift Selection Search - Swiftly access your search engines in a popup panel when you select text in a webpage.
Yase - Yase is a privacy friendly search engine
ContextSearch web-ext - Search for selection with your browser's search engines via a pop-up.
Bing - Bing helps you turn information into action, making it faster and easier to go from searching to doing.