When add-on bar is disabled, restarting Firefox will leave a white bar where add-on bar was.

I like to have the add-on bar disabled to allow more page viewing space. Quite often when I open Firefox, there is a white bar in the same location where the add-on bar should be (if it was enabled). If I enable the add-on bar and disable it, it goes away. This is more of an annoyance than anything else.