I'm running version: 2011031901

This link: http://piro.sakura.ne.jp/xul/xpi/confirm.cgi?treestyletab.xp...

gives me: Forbidden Installation You don't have a permission to install XPI package directly from other websites. You have to access this extension from the home page of itself.

Am I doing something wrong?

What you have appears to be the latest version (similar to what I have). Weird that I didn’t see that warning though. Which OS are you on? (I am on a mac)

I'm on Windows 7 - 64

I imagine it will get worked out, but its not until something fails that you realize your dependence.