diff -r 000000000000 -r 6474c204b198 browser/devtools/netmonitor/test/browser_net_large-response.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/devtools/netmonitor/test/browser_net_large-response.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,51 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+/**
+ * Tests if very large response contents are just displayed as plain text.
+ */
+
+function test() {
+  initNetMonitor(CUSTOM_GET_URL).then(([aTab, aDebuggee, aMonitor]) => {
+    info("Starting test... ");
+
+    // This test could potentially be slow because over 100 KB of stuff
+    // is going to be requested and displayed in the source editor.
+    requestLongerTimeout(2);
+
+    let { document, Editor, NetMonitorView } = aMonitor.panelWin;
+    let { RequestsMenu } = NetMonitorView;
+
+    RequestsMenu.lazyUpdate = false;
+
+    waitForNetworkEvents(aMonitor, 1).then(() => {
+      verifyRequestItemTarget(RequestsMenu.getItemAtIndex(0),
+        "GET", CONTENT_TYPE_SJS + "?fmt=html-long", {
+          status: 200,
+          statusText: "OK"
+        });
+
+      aMonitor.panelWin.once(aMonitor.panelWin.EVENTS.RESPONSE_BODY_DISPLAYED, () => {
+        NetMonitorView.editor("#response-content-textarea").then((aEditor) => {
+          ok(aEditor.getText().match(/^<p>/),
+            "The text shown in the source editor is incorrect.");
+          is(aEditor.getMode(), Editor.modes.text,
+            "The mode active in the source editor is incorrect.");
+
+          teardown(aMonitor).then(finish);
+        });
+      });
+
+      EventUtils.sendMouseEvent({ type: "mousedown" },
+        document.getElementById("details-pane-toggle"));
+      EventUtils.sendMouseEvent({ type: "mousedown" },
+        document.querySelectorAll("#details-pane tab")[3]);
+    });
+
+    aDebuggee.performRequests(1, CONTENT_TYPE_SJS + "?fmt=html-long");
+  });
+
+  // This test uses a lot of memory, so force a GC to help fragmentation.
+  info("Forcing GC after netmonitor test.");
+  Cu.forceGC();
+}