Unpaywall - browser extension for legally accessing articles behind paywalls

Adds a tab to some browsers that links you through to LEGALLY uploaded full-text versions of articles - for example when you are looking at an abstract where the main article is behind a paywall. The legal copies are pulled from institutional repositories, authors' websites etc. 

See http://unpaywall.org/faq for further details of this tool, which is an add-on for Chrome and Firefox browsers at the time of posting.