RSS button in firefox

[boatdesign]

As an RSS newbie, I just noticed that on the vbulletin.com forum here a button appears in the firefox status bar "RSS" that allows one to subscribe to the RSS feed. If you put this on your bookmark toolbar for example, you get a live dropdown with the newest x threads - pretty neat! On my own forum I do have RSS enabled under external data provider, but no button appears in firefox. How come? Something new about the 3.5 RSS feed?

[Jake Bunce]

It appears that is being generated by this code in the headinclude template:

<link rel="alternate" type="application/rss+xml" title="vBulletin Community Forum RSS Feed" href="external.php?type=RSS" />