Recently both Firefox and Chrome have added a security feature called
"Click-to-play"" When enabled, it prevents certain plug-ins like Adobe
Flash, Java, and Microsoft Silverlight from automatically running as you
browse websites. In addition to providing greater security, blocking Flash
and other plug-ins makes browsing faster. Here's how to enable this feature
in Chrome and Firefox.
http://www.techsupportalert.com/content/how-be-safer-and-speed-your-surfing-new-security-feature-firefox-and-chrome-browsers.htm