steps to reproduced:
1 Load the applet inside the browser: http://sqeweb.us.oracle.com/deployment1/deployment_6_UR_int_exec_ws/6/deployment/src/javafx/fxfeaturesTest/fxfeaturesTest/html/FullscreenTest.html
2 There we are going to be 2 stages one running inside the browser and one outside the browser.
3 Click 'Toggle Fullscreen' on stage embedded within the browser
4 Make sure that application is getting full screened i.e covering the entire screen
5 Use ALT+TAB to Switch to secondary stage window.
If the original Full screen went back to browser, then the bug reproduced.