Created attachment 394057 [details] screen cast I've attached a screen cast which is hopefully more descriptive than this text. Stuart suggested that this is related to compositor.
Likely a dup of: https://bugzilla.mozilla.org/show_bug.cgi?id=506517 Are you running the latest builds ? Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2a2pre) Gecko/20090812 Minefield/3.6a2pre Firefox/3.6 (.NET CLR 3.5.30729) ID:20090812094025
apparently, I'm not: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2a1pre) Gecko/20090724 Minefield/3.6a1pre (.NET CLR 3.5.30729)