This is a C&P from another forum that I thought was interesting ... "As was pointed out to me on IRC it's now confirmed: Mozilla's decision has been made to remove support for Themes from Firefox (and potentially derivative products as a result). Benjamin Smedberg wrote: "As part of Firefox great-or-dead, we've decided to stop support for "heavyweight" themes which can do arbitrary styling and replace chrome packages." You like your Noia, FT DeepDark and similar themes for your browser? Sorry if you're using Firefox (and direct clones) -- once this lands, support for what Mozila calls "heavyweight themes" will be gone. You'll have the Mozilla way (maybe with custom toolbar backgrounds AKA personas AKA lightweight themes) or the highway to choose from."