Currently, if I don't update Nightly every day, I wind up having to do two updates to get caught up. When I go into the about window, it should either do a fresh check for updates if the currently downloaded update is dated anytime older than today, or it should always check for a newer copy when you click the apply button. Because starting Firefox up can be a sluggish process (especially with lots of tabs and windows), having to do it twice in a row can be a tedious situation that causes one to avoid updating until it can no longer be avoided.