var label = aPopup.firstChild;
          label.setAttribute("value", tab.getAttribute("label"));

          var canvas = aPopup.lastChild.firstChild;

          if (!this.mPrefs.getBoolPref("browser.tabs.tooltippreview.enable")) {
            canvas.parentNode.hidden = true;
+           label.removeAttribute("width");
            return true;
          }

          var ctx;
          try {
            ctx = canvas.getContext("2d");
          } catch (e) {
            return true;
          }

+         label.setAttribute("width", 0);
          var win = b.contentWindow;
          var w = win.innerWidth;
          var h = win.innerHeight;