Ever since flash player 26 this started happening to me. If I open a flash game in a new tab to let it load while I continue browsing, when I go to the tab it has a (usually) white "overlay" over the flash content. It's easily dispelled when I open the settings but it's growing annoying. It only happens on Firefox. Only with flash content, and only when loaded in an inactive tab. I've never had this issue before flash 26. Been hoping it will fix itself. But despite major updates in both flash and Firefox the problem persists.
EDIT: A game I was loading today had an image as a background and I could see that between the strips of flash that appeared so it's not an overlay but the background that shows through.
Yeah, this has something to do with areas of the screen not getting redrawn. If I move my mouse through the affected area, then it gets redrawn as the mouse cursor is drawn and removed...
I'll get a bug opened.
Thanks a lot for looking in to it! I hope it gets resolved soon!