Regardless of what sites I am browsing the screen can get corrupted, including menu bars, download windows, etc. This also includes minimizing Firefox to go do something else in Windows, and all or part of the Firefox screen will pop back up, but will be more like a "ghost image" of it, i.e. mousing over things will reveal what *should* be there, making that part of the Firefox ghost-image disappear. This also happens to a lesser extent with Thunderbird.