diff -r 000000000000 -r 6474c204b198 browser/devtools/sourceeditor/codemirror/trailingspace.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/devtools/sourceeditor/codemirror/trailingspace.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,24 @@
+(function(mod) {
+  if (typeof exports == "object" && typeof module == "object") // CommonJS
+    mod(require("../../lib/codemirror"));
+  else if (typeof define == "function" && define.amd) // AMD
+    define(["../../lib/codemirror"], mod);
+  else // Plain browser env
+    mod(CodeMirror);
+})(function(CodeMirror) {
+  CodeMirror.defineOption("showTrailingSpace", false, function(cm, val, prev) {
+    if (prev == CodeMirror.Init) prev = false;
+    if (prev && !val)
+      cm.removeOverlay("trailingspace");
+    else if (!prev && val)
+      cm.addOverlay({
+        token: function(stream) {
+          for (var l = stream.string.length, i = l; i && /\s/.test(stream.string.charAt(i - 1)); --i) {}
+          if (i > stream.pos) { stream.pos = i; return null; }
+          stream.pos = l;
+          return "trailingspace";
+        },
+        name: "trailingspace"
+      });
+  });
+});