It's a pretty darn good tool for people like me who don't know how to create/edit style sheets. The big problem is something I have seen in past on other style tools on other platforms. It would be so much more helpful if you provided a simple numbered MARKUP diagram that shows exactly where within the browser tabs and toolbars each of the adjustable color elements exist. Only about 5 or 6 adjustment tools are super-obvious about where this color will get applied, such as "Active Tab" background color, or color of Icons. But far too many of the elements are very non-obvious to end users who didn't write the Firefox Color tool. YES it's great that some (but only very few) UI elements actually "light up" in the simplified preview element as you make a change. Either do it for all the elements or its huge disservice. ... I should really subtract a 2nd star for the non-obvious way to RE-APPLY your theme when buggy things happen that suddenly strip out the entire theme reverting to default. You show how to SAVE, how to favorite, how to share, but missing a simple actuator to "Re-apply theme".