code: function waitForGeckoLinkLoaded() {
            wait(function () {
              try {
                // Accessing the cssRules will throw an exception until the CSS file is loaded
                var cssRules = style.sheet.cssRules;
                passed();
                return !!cssRules;
              } catch (ex) {
                // Ignore
              }
            }, waitForGeckoLinkLoaded);
          }
docs: Workaround for older Geckos that doesn't have any onload event for StyleSheets