Plug-ins help browsers process special types of content, such as Java files.  Since plug-ins can sometimes be a security risk, Chrome now blocks plug-ins that are not widely used.  When a plug-in is blocked you will receive a message like the one below:

If you see a message bar within Chrome that says The Java plug-in needs your permission to run, you can perform one of the following actions:

• Click the Run this time button to allow the Java content on the page to run until you leave the page.
  
• Click Always run on this site to allow Java to run on all the site's pages. You will not see this message again for pages on the site you allowed.