@namespace url(http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul);

@-moz-document url(chrome://browser/content/browser.xul) 
{

  tabbrowser[treestyletab-style~="square"][treestyletab-mode="vertical"]:not([treestyletab-style~="vertigo"])
  .tabbrowser-tab + .tabbrowser-tab:not([selected]) {
    background-color: rgb(243, 245, 247) !important;
    }

  tabbrowser[treestyletab-style~="square"][treestyletab-mode="vertical"]:not([treestyletab-style~="vertigo"])
  .tabbrowser-tab:not([selected]) {
    background-color: rgb(243, 245, 247) !important;
    }

  tabbrowser[treestyletab-mode="vertical"] .tabbrowser-tab {
    border-top: none !important;
    border-bottom-width: 1px !important;
    }

}