The Jiffie-Plugin uses Internet Explorer to execute the test cases. This means that if it runs in IE, then it can be tested in IE.
The disatvantage of this approach is that you are restricted to executing your tests only on a windows machine running IE.
As the name implies, the Jiffie plug-in uses Jiffie. Jiffie then uses Jacob, a Java-COM interface that can be used to test Windows applications through Java. This plug-in is licensed under the GPL and has been separated from the jameleon-core source code due to the licensing of Jiffie and Jacob.