diff -r 000000000000 -r 6474c204b198 editor/reftests/xul/platform.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/editor/reftests/xul/platform.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,28 @@
+// The appearance of XUL elements is platform-specific, so we set the
+// style of the root element according to the platform, so that the
+// CSS code inside input.css can select the correct styles for each
+// platform.
+
+var id;
+var ua = navigator.userAgent;
+
+if (/Windows/.test(ua)) {
+  id = "win";
+  if (/NT 5\.1/.test(ua) || /NT 5\.2; Win64/.test(ua))
+    var classname = "winxp";
+}
+else if (/Linux/.test(ua))
+  id = "linux";
+else if (/SunOS/.test(ua))
+  id = "linux";
+else if (/Mac OS X/.test(ua))
+  id = "mac";
+
+if (id)
+  document.documentElement.setAttribute("id", id);
+else
+  document.documentElement.appendChild(
+    document.createTextNode("Unrecognized platform")
+  );
+if (classname)
+  document.documentElement.setAttribute("class", classname);