Eriisa: It is actually because Firefox is quicker to load pages then other browsers which sometimes mess up BrainKing a little.
Since Firefox will start showing a page before it is completely loaded, what it does first is show the left column, then it load the middle column (moving over the far left column), then it will load the right column (again, moving over the other 2 columns) - causing it to look like the screen is "jumping" around.
Only sites like BrainKing which use columns will you see this. Plus if you are on a fast enough connection, you rarely see it.