Like the default Firefox theme, but find it to be a little too colorful for its own good? Then you might want to check out the Firefox theme – MonoChrome. It brings Firefox back to basics with everything turned black and white and grey all over.
MonoChrome, simply put – is a monochrome version of the default Windows theme for Firefox 3.6, otherwise known as the "Strata" theme. To the theme creator’s credit, he has done a fantastic job at re-themeing this creative take on the default Firefox theme – and it shows.
The goal here is to create a lightweight, aesthetically pleasing theme – and MonoChrome does it.
You can pick up MonoChrome from the Firefox Add-ons website.