A vulnerability has been reported in Yahoo Toolbar by Security Researcher, which causes cross site scripting flaw on popular websites like Flickr, Yahoo, Google, Pinterest, Youtube, Amazon, Twitter and many more. Yahoo offers a web browser toolbar which includes apps for leading sites like Facebook, Yahoo! Mail, Weather and News. The vulnerability resides in the way Toolbar intercepts and modifies the website pages in the browser to deliver additional content. The flaw could be used to redirect, infect or cookie stealing using Cross Site Scripting attacks.
Source: https://thehackernews.com/2014/06/yahoo-toolbar-vulnerability-triggers_10.html