The author's site has the latest version that works with FF4.
http://piro.sakura.ne.jp/xul/_treestyletab.html.en
DL: http://piro.sakura.ne.jp/xul/xpi/confirm.cgi?treestyletab.xp...
DL: http://piro.sakura.ne.jp/xul/xpi/confirm.cgi?treestyletab.xp...
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?
I imagine it will get worked out, but its not until something fails that you realize your dependence.