diff -r 000000000000 -r 6474c204b198 browser/devtools/styleeditor/test/browser_styleeditor_sourcemaps.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/devtools/styleeditor/test/browser_styleeditor_sourcemaps.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,125 @@
+/* vim: set ts=2 et sw=2 tw=80: */
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+// https rather than chrome to improve coverage
+const TESTCASE_URI = TEST_BASE_HTTPS + "sourcemaps.html";
+const PREF = "devtools.styleeditor.source-maps-enabled";
+
+
+const contents = {
+  "sourcemaps.scss": [
+    "",
+    "$paulrougetpink: #f06;",
+    "",
+    "div {",
+    "  color: $paulrougetpink;",
+    "}",
+    "",
+    "span {",
+    "  background-color: #EEE;",
+    "}"
+  ].join("\n"),
+  "contained.scss": [
+    "$pink: #f06;",
+    "",
+    "#header {",
+    "  color: $pink;",
+    "}"
+  ].join("\n"),
+  "sourcemaps.css": [
+    "div {",
+    "  color: #ff0066; }",
+    "",
+    "span {",
+    "  background-color: #EEE; }",
+    "",
+    "/*# sourceMappingURL=sourcemaps.css.map */"
+  ].join("\n"),
+  "contained.css": [
+    "#header {",
+    "  color: #f06; }",
+    "",
+    "/*# sourceMappingURL=data:application/json;base64,eyJ2ZXJzaW9uIjozLCJmaWxlIjoiIiwic291cmNlcyI6WyJzYXNzL2NvbnRhaW5lZC5zY3NzIl0sIm5hbWVzIjpbXSwibWFwcGluZ3MiOiJBQUVBO0VBQ0UsT0FISyIsInNvdXJjZXNDb250ZW50IjpbIiRwaW5rOiAjZjA2O1xuXG4jaGVhZGVyIHtcbiAgY29sb3I6ICRwaW5rO1xufSJdfQ==*/"
+  ].join("\n")
+}
+
+const cssNames = ["sourcemaps.css", "contained.css"];
+const scssNames = ["sourcemaps.scss", "contained.scss"];
+
+waitForExplicitFinish();
+
+let test = asyncTest(function*() {
+  Services.prefs.setBoolPref(PREF, true);
+
+  let {UI} = yield addTabAndOpenStyleEditors(5, null, TESTCASE_URI);
+
+  is(UI.editors.length, 3,
+    "correct number of editors with source maps enabled");
+
+  // Test first plain css editor
+  testFirstEditor(UI.editors[0]);
+
+  // Test Scss editors
+  yield testEditor(UI.editors[1], scssNames);
+  yield testEditor(UI.editors[2], scssNames);
+
+  // Test disabling original sources
+  yield togglePref(UI);
+
+  is(UI.editors.length, 3, "correct number of editors after pref toggled");
+
+  // Test CSS editors
+  yield testEditor(UI.editors[1], cssNames);
+  yield testEditor(UI.editors[2], cssNames);
+
+  Services.prefs.clearUserPref(PREF);
+});
+
+function testFirstEditor(editor) {
+  let name = getStylesheetNameFor(editor);
+  is(name, "simple.css", "First style sheet display name is correct");
+}
+
+function testEditor(editor, possibleNames) {
+  let name = getStylesheetNameFor(editor);
+  ok(possibleNames.indexOf(name) >= 0, name + " editor name is correct");
+
+  return openEditor(editor).then(() => {
+    let expectedText = contents[name];
+
+    let text = editor.sourceEditor.getText();
+    is(text, expectedText, name + " editor contains expected text");
+  });
+}
+
+/* Helpers */
+
+function togglePref(UI) {
+  let deferred = promise.defer();
+  let count = 0;
+
+  UI.on("editor-added", (event, editor) => {
+    if (++count == 3) {
+      deferred.resolve();
+    }
+  })
+
+  Services.prefs.setBoolPref(PREF, false);
+  return deferred.promise;
+}
+
+function openEditor(editor) {
+  getLinkFor(editor).click();
+
+  return editor.getSourceEditor();
+}
+
+function getLinkFor(editor) {
+  return editor.summary.querySelector(".stylesheet-name");
+}
+
+function getStylesheetNameFor(editor) {
+  return editor.summary.querySelector(".stylesheet-name > label")
+         .getAttribute("value")
+}