Please be aware that this add-on is not open source.
As an alternative I found Violent Monkey which is open source and seems to work just as fine. Also, every userscript you install may be spyware. Be careful!

這是一個無論你是低手亦或是網頁編程高手都必備的插件,它能讓你的瀏覽成為一種你想要的隨心所欲!只有你想不到的沒有它做不到的.

Good broser