Yet one more reason why I'm glad I moved to PaleMoon. via Mozilla to remove Themes from Firefox
1222546 – Product plan: remove support for heavyweight themes
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.
And in case of the inevitable questions from people who still don't understand what Pale Moon is and is not: No, this will not in any way impact Pale Moon. We pride ourselves on having a nice and growing collection of complete themes.
Solutions born from paranoia are never the best solutions. -MC
1222546 – Product plan: remove support for heavyweight themes