Zotero is a citation management tool that works with Firefox and Chrome (and limited Safari functionality).
It has a desktop program with a web backup. The Zotero Connector recognizes and extracts citation information from websites, library catalogs, and databases. It enables you to easily save, organize, and create bibliographies of the sources you collect.
Zotero is powerful, easy-to-use, and free. It now works with Google Docs.