I've been using the Firefox addon called "Tree Style Tab" for quite a few years now. I'm quite pleased with it since I have more width than height on my screen anyway.
Just a heads up!
Just a heads up!
Now somebody else can inform me about the newest one.
#sidebar-box[sidebarcommand="treestyletab_piro_sakura_ne_jp-sidebar-action"] #sidebar-header { display: none; }