If you dont want the jdeveloper select role screen to pop up each time you start jdeveloper uncheck the Always prompt for role selection on startup click OK and jdeveloper should launch.
Using the APIs provided by the Extension SDK developers can add components that range from a new menu option through a wizard and up to a complete new editor.
Extensions can be exposed through JDevelopers Check-for-Updates functionality for easy one click install.
These are available for download through the help-check for updates menu option in JDeveloper.
Compare chrome and firefox for mac osFurther support is provided through the JDeveloper discussion forum.
Gross beat free vstA quick demo of building extensions for JDeveloper 11gR2 is here, and for 11gR1 here.
For 11gR2 you can find a new Developers Guide for Oracle JDeveloper Extensions.