[NOT AN ISSUE] Suggestion for images (Priority Level: Low)

[EstherMoellman]

Inside your package add-on ({7c7f6dea-3957-4bb9-9eec-2ef2b9e5bcec}.xpi), image files like "bg.jpg", "2x.png", "38.png", "48.png", "logo.png" etc... are responsible for most of the size of the add-on.

You can dramatically reduce that in the future (it is not a priority now) if you use svg files (instead png etc). This simple detail will make UltimaDark the smaller darkening add-on in the market. IMHO, in underlines, this small size will show more simplicity for UltimaDark, indirectly also implying focus on less and less browser performance impact.

[Vintagemotors]

Changing to SVG is definitely doable, it may even be something I could port for you at least partially (I've done some work with SVG)- I think focusing on performance makes sense given UltimaDark is currently a massive performance leader compared to every other extension I have tested.