I didn't comment on dougees version since the labels weren't transparent. So I made some of my own since the white bg didn't match my theme. I also lost the @-moz-document deal, it's not needed and using "Applies to XUL" will work. The stylish tree is ID'd so all you need is #styles > treechildren::-moz-tree-checkbox for it to work in the manage window as well as the sidebar.
Greg S said about Stylish Manager enabled/disabled text Mod on May 13 2006
FirefoxWiz said about Stylish Manager enabled/disabled text Mod on Apr 25 2006
Julian said about Stylish Manager enabled/disabled text Mod on Apr 10 2006