uhh that's weird, it loads the install prompt for me
Did you turn Greasemonkey on? It might be disabled by default, there should be a monkey icon at the bottom right of FireFox to indicate whether it's on or not (grey for off, colored for on).
Oh yeah, also the addon compatibility reporter is necessary, it'll keep your addons working in future FireFox updates.
https://addons.mozilla.org/en-US/firefox/addon/add-on-compatibility-reporter/
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