Those of you who are on Mac OS may have noticed that many Greenfoot scenarios flicker really badly when run in a browser. This is caused by an Apple applet implementation change some months ago. At least Chrome and Safari are affected, maybe other browsers as well (I haven't tried). Here is what you can do about it: With the applet web page open, click on the applet, then hold down the Command (cmd) key. A title bar appears on top of the applet. Grab the applet by this title bar and drag it out of the browser window. It will get its own window and run beautifully.