diff -r 000000000000 -r 6474c204b198 browser/devtools/debugger/test/browser_dbg_reload-preferred-script-03.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/devtools/debugger/test/browser_dbg_reload-preferred-script-03.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,59 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+/**
+ * Tests if the preferred source is shown when a page is loaded and
+ * the preferred source is specified after another source was definitely shown.
+ */
+
+const TAB_URL = EXAMPLE_URL + "doc_script-switching-01.html";
+const FIRST_URL = EXAMPLE_URL + "code_script-switching-01.js";
+const SECOND_URL = EXAMPLE_URL + "code_script-switching-02.js";
+
+let gTab, gDebuggee, gPanel, gDebugger;
+let gSources;
+
+function test() {
+  initDebugger(TAB_URL).then(([aTab, aDebuggee, aPanel]) => {
+    gTab = aTab;
+    gDebuggee = aDebuggee;
+    gPanel = aPanel;
+    gDebugger = gPanel.panelWin;
+    gSources = gDebugger.DebuggerView.Sources;
+
+    waitForSourceShown(gPanel, FIRST_URL)
+      .then(() => testSource("", FIRST_URL))
+      .then(() => switchToSource(SECOND_URL))
+      .then(() => testSource(SECOND_URL))
+      .then(() => switchToSource(FIRST_URL))
+      .then(() => testSource(FIRST_URL))
+      .then(() => closeDebuggerAndFinish(gPanel))
+      .then(null, aError => {
+        ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
+      });
+  });
+}
+
+function testSource(aPreferredUrl, aSelectedUrl = aPreferredUrl) {
+  info("Currently preferred source: " + gSources.preferredValue);
+  info("Currently selected source: " + gSources.selectedValue);
+
+  is(gSources.preferredValue, aPreferredUrl,
+    "The preferred source url wasn't set correctly.");
+  is(gSources.selectedValue, aSelectedUrl,
+    "The selected source isn't the correct one.");
+}
+
+function switchToSource(aUrl) {
+  let finished = waitForSourceShown(gPanel, aUrl);
+  gSources.preferredSource = aUrl;
+  return finished;
+}
+
+registerCleanupFunction(function() {
+  gTab = null;
+  gDebuggee = null;
+  gPanel = null;
+  gDebugger = null;
+  gSources = null;
+});