Weird message regarding the Firefox 'Friendbar' add-on

I have noticed something funny and weird today.

Friendbar (https://addons.update.mozilla.org/en-US/firefox/addon/10223), the cool add-on for firefox 'seems not available for linux' when you try to install it on your firefox using Linux(Ubuntu).

But when i download the extension on windows and copy it in my firefox profile on Linux it works like a charm :-).

So my doubt now is about the message I read; is the add-on really available for linux or not (or maybe sometimes it's available and sometimes not) ?

Can you tell me ? yes you why are you smiling, if you know just answer ...