Whenever I disable tree-style tabs, I can see the tabs at the top of the window. After I install it, I can't see it once more. :( This started accidentally after a random sequence of keys were pressed by a child I was babysitting (not well enough, apparently). I'm on a Mac (Mavericks), and I tried to do a clean install. I moved Firefox to trash, emptied the trash, and deleted the plist files from the ~/Library/Preferences folder, but when I reinstalled the same problem occurred. I suspect, however, that something was still retained because when I reinstalled Firefox, my 1Password add-on was magically already present. Any suggestions? Thanks!