When there is a shockwave flash video embedded inside an object tag, and the page gets loaded with a scroll position (such as scrolling, then reload, or do back/forward), there is a whole mess of black over most of the page on the initial paint. Repaints after that point are correct, so scrolling displays new content correctly. This only happens if the scroll position is set at the time of the initial reflow. If the document loads too slow, you don't see it. I will attach a simplified testcase. I'm not sure about the component, but my first guess is Views. I'm marking this as major severity because it will most often be triggered by ads, and that's quite annoying.

Load this file, scroll down, then reload, and you should see the problem. If you take out the <object> tag, it won't happen.

Oh, forgot to say, I saw this on Mozilla 1.0RC2.

This problem went away in RC3. Marking WORKSFORME.