However with this tweak you can make buttons disappear completely in images only mode on your toolbar, or no icon for images and text modes.
First up, open up skin.ini in any of the skins zip files.
This removes any padding or margin left or right, so there isn't any space.
[Toolbar Button Skin.disabled] Padding Left = 0 Padding Right = 0 Margin Right = 0 Margin Left = 0
Create a seperate section for Back(for example that gets disabled when no back available)
[Back.disabled] Width=0 Height=0
For the rest, clone the Back.disabled section and its done.
[Forward.disabled] Clone = Back.disabled [Stop.disabled] Clone = Back.disabled [Fast Forward.disabled] Clone = Back.disabled [Wand.disabled] Clone = Back.disabled [Trash.disabled] Clone = Back.disabled
These will disable the icons for Forward, Stop, Fast Forward, Wand and Trash respectively.