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.
Context Search - Context Search is a Firefox extension that expands the context menu's 'Search for' item...
ContextSearch web-ext - Search for selection with your browser's search engines via a pop-up.
SearchWP for Firefox - Jump-to-word buttons and highlighting for the search box content
Selection Search - With this extension you can easily search for text you have selected.
SearchWP - Instantly improve the search experience of your WordPress site today with SearchWP, the best WordPress search plugin you can find!