I'm using Firefox 0.9 on XP at work. I used to be able to istall extensions fine, and have a couple of good ones installed. But now when I try to install a new extension, nothing happens. I go to the Extensions page, find one I want, and click the Install Link button. The browser pauses for half a second but nothing installs or downloads. This is for all of the available extensions. There's nothing in Help about this problem. How do I make it work again?