Why add an extension without Firefox functionality to the Firefox Add-Ons store?

doesn't work on firefox :( my spotify looks boring without the background PLEASE update this!!!!

Works great on chromium, but sadly on firefox doesn't work at all

Works on chrome (V2.1 of this add-on), but doesn't work on Firefox (V1.6.2 beta "), the developer should update the extension.

Lacks almost all functionality in this firefox version. I use this on chromium based browsers and it looks great! Please update this extension.