--- a/browser/components/customizableui/CustomizableWidgets.jsm
+++ b/browser/components/customizableui/CustomizableWidgets.jsm
@@ -312,17 +312,17 @@ const CustomizableWidgets = [
       obnode.setAttribute("attribute", "syncstatus");
       aNode.appendChild(obnode);
 
       // A somewhat complicated dance to format the mobilepromo label.
       let bundle = doc.getElementById("bundle_browser");
       let formatArgs = ["android", "ios"].map(os => {
         let link = doc.createElement("label");
         link.textContent = bundle.getString(`appMenuRemoteTabs.mobilePromo.${os}`)
-        link.href = Services.prefs.getCharPref(`identity.mobilepromo.${os}`) + "synced-tabs";
+        link.setAttribute("href", Services.prefs.getCharPref(`identity.mobilepromo.${os}`) + "synced-tabs");
         link.className = "text-link remotetabs-promo-link";
         return link.outerHTML;
       });
       // Put it all together...
       let contents = bundle.getFormattedString("appMenuRemoteTabs.mobilePromo", formatArgs);
       doc.getElementById("PanelUI-remotetabs-mobile-promo").innerHTML = contents;
     },
     onViewShowing(aEvent) {