Be careful with old versions!
These versions are displayed for reference and testing purposes. You should always use the latest version of an add-on.
Also fixed the styles that used to make obvious where the dragged toolbar was going to be inserted, that stopped working with 3.0.?
Please do not complain that it does not allow to merge two sidebars ! It does not pretend to !
To merge sidebar elements, use the Firefox customize default menu item.
The drag handles appears when you unlock the toolbars, and disappear when you lock them back.