Algolia - Algolia's Search API makes it easy to deliver a great search experience in your apps & websites. Algolia Search provides hosted full-text, numerical, faceted and geolocalized search.
Swift Selection Search - Swiftly access your search engines in a popup panel when you select text in a webpage.
ElasticSearch - Elasticsearch is an open source, distributed, RESTful search engine.
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.
Swiftype Site Search - Swiftype Site Search helps to sell more, get the right answer to more people on the platform and surface relevant content for readers and followers.
Trufflepiggy - Context Search - The context menu search for all of us: quick, easy & customizable. Best in class group-search: find on multiple sites at once! Supports favicons (Firefox), omnibox & cross browser sync. Select from 1000+ user generated searches or add your own.