Bookmarklets
Bookmarklets or Favelets(in IE) small JavaScript snippets that is used to automate some actions.
They are created using the ability to execute javascript code using the 'javascript:' pseudo protocol in URL.
Installing and Using
To install a bookmarklet just drag the bookmarklet to your Bookmarks Toolbar(Firefox) or Links Bar(IE).
To run this script browse to any page and click on this bookmark. The script will be executed in the current page's context.