autohiding toolbars: Wait for [sessionrestored] before setting urlbar transition --urlbar-container-height, which is set for #urlbar-container, is computed dynamically early on startup. If we set transition to it, then it will transition from the initial height to the new value and because of that the computed value is determined using the initial height instead of the "correct" value set by toolbar density options. The issue most noticeably occurs when initial window has startup page as blank, and when compact density is selected, but it does but really it can also happen without them, the effect just might be so subtle that it's not perceivable.