the extension itself deserves 5 stars - but, I have a dark them in my firefox and there is no guideline from this author how to change the css for this addon. It is as default black, so I cannot see the icon at all. I moved it to a spot where I know it should be, but this should not be so hard to offer a white or grey version of this addon.
If this author comes up with instructions at least how I can get that changed so I can actually see the + sign, I will change my vote immediately to 5 stars