diff -r 000000000000 -r 6474c204b198 browser/devtools/debugger/test/browser_dbg_tracing-06.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/devtools/debugger/test/browser_dbg_tracing-06.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,39 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+/**
+ * Test that the tracer doesn't connect to the backend when tracing is disabled.
+ */
+
+const TAB_URL = EXAMPLE_URL + "doc_tracing-01.html";
+const TRACER_PREF = "devtools.debugger.tracer";
+
+let gTab, gDebuggee, gPanel, gDebugger;
+let gOriginalPref = Services.prefs.getBoolPref(TRACER_PREF);
+Services.prefs.setBoolPref(TRACER_PREF, false);
+
+function test() {
+  initDebugger(TAB_URL).then(([aTab, aDebuggee, aPanel]) => {
+    gTab = aTab;
+    gDebuggee = aDebuggee;
+    gPanel = aPanel;
+    gDebugger = gPanel.panelWin;
+
+    waitForSourceShown(gPanel, "code_tracing-01.js")
+      .then(() => {
+        ok(!gDebugger.DebuggerController.traceClient, "Should not have a trace client");
+        closeDebuggerAndFinish(gPanel);
+      })
+      .then(null, aError => {
+        ok(false, "Got an error: " + aError.message + "\n" + aError.stack);
+      });
+  });
+}
+
+registerCleanupFunction(function() {
+  gTab = null;
+  gDebuggee = null;
+  gPanel = null;
+  gDebugger = null;
+  Services.prefs.setBoolPref(TRACER_PREF, gOriginalPref);
+});