为啥我这个版本安不了add-on?

在https://addons.mozilla.org/里点击安装显示
To install Nightly Tester Tools and thousands of other Firefox add-ons, get Firefox, a free and open web browser from Mozilla. To learn more about Firefox and how it can make your internet experience better, click the button below.
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(第一次用Alpha版.. )  大家指教下哦