Question pretty much sums it up. Windows Title bar keeps flitting in and out, causing screen to jump. Concurrently, right and bottom window margins resize a bit smaller. No apparent rhyme or reason, but leads to a lot of bad mouse clicks. Unrelated to whether the bookmarks tab is open or not. Happens in safemode as well, and my theme is the default. I don't want a plug-in to fix this, I want Firefox 5.0 to behave properly on its own.