Trying to use a scale widget in a prefwindow where you need to set a minimum value > 0 will overwrite the preference setting with that minimum when the window is opened. The problem is that the scale widget sets its value to the minimum in its constructor, this dispatches a change event which the prefpane catches and uses to set the preference value, before the prefwindow code has had a chance to tell the scale what its initial value really is. To use a scale in a prefwindow you need to set preference-editable="true" on it, which we probably should fix too.
seems resolved in 22.214.171.124 (works for me)
I just ran into this in latest Firefox 4 nightly, so this is still a problem.