If your looking for a mostly 2D, grayscale and compact theme for your Firefox browsing ways – look no further than the Two Dimensions theme. As you can see with the screenshot I included, it is a very slick skin for your Firefox browsing ways that will not disappoint those of you who like to keep things simple.
It would fit nicely, I think, in my list of lightest popular themes for Firefox. Who knows, it might earn its spot soon enough.
Thus far a five-star theme, that is rising in the ranks, you can pick up Two Dimensions and add it to your own Firefox installation at the Firefox Add-ons web site.