In reader, Edit, Preferences, Internet, Uncheck "Display PDF in Browser" so PDF files will open in a reader window.
Open a PDF file from any web page. The PDF opens in Reader as it should, but Fireflx also opens a new page in the same window, containing the PDF's location in the address bar.
This new page now copies the image of any windows that appears in front of it, starting with the contents of the PDF itself: If you drag the front window around, it strobes copies of itself onto the new Firefox page. The only way to clear this annoying page is to close it, or hit the back button if available
(Before reader 9, FF just opened a blank page that didn't copy anything.)
The sample below was made by opening a PDF, alt-tabbing back to Firefox, then dragging a small window around on top of it.
The gray background is from MS Paint, whch had been opened on top of the Firefox window prior to generating the screen capture.
Anyone else seeing this? Please give it a try (This does not occur in IE)