diff -r 000000000000 -r 6474c204b198 browser/devtools/netmonitor/test/browser_net_icon-preview.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/devtools/netmonitor/test/browser_net_icon-preview.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,61 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+/**
+ * Tests if image responses show a thumbnail in the requests menu.
+ */
+
+function test() {
+  initNetMonitor(CONTENT_TYPE_WITHOUT_CACHE_URL).then(([aTab, aDebuggee, aMonitor]) => {
+    info("Starting test... ");
+
+    let { $, $all, EVENTS, ACTIVITY_TYPE, NetMonitorView, NetMonitorController } = aMonitor.panelWin;
+    let { RequestsMenu } = NetMonitorView;
+
+    promise.all([
+      waitForNetworkEvents(aMonitor, 6),
+      waitFor(aMonitor.panelWin, EVENTS.RESPONSE_IMAGE_THUMBNAIL_DISPLAYED)
+    ]).then(() => {
+      info("Checking the image thumbnail when all items are shown.");
+      checkImageThumbnail();
+
+      RequestsMenu.sortBy("size");
+      info("Checking the image thumbnail when all items are sorted.");
+      checkImageThumbnail();
+
+      RequestsMenu.filterOn("images");
+      info("Checking the image thumbnail when only images are shown.");
+      checkImageThumbnail();
+
+      info("Reloading the debuggee and performing all requests again...");
+      reloadAndPerformRequests();
+
+      return promise.all([
+        waitForNetworkEvents(aMonitor, 7), // 6 + 1
+        waitFor(aMonitor.panelWin, EVENTS.RESPONSE_IMAGE_THUMBNAIL_DISPLAYED)
+      ]);
+    }).then(() => {
+      info("Checking the image thumbnail after a reload.");
+      checkImageThumbnail();
+
+      teardown(aMonitor).then(finish);
+    });
+
+    function reloadAndPerformRequests() {
+      NetMonitorController.triggerActivity(ACTIVITY_TYPE.RELOAD.WITH_CACHE_ENABLED).then(() => {
+        aDebuggee.performRequests();
+      });
+    }
+
+    function checkImageThumbnail() {
+      is($all(".requests-menu-icon[type=thumbnail]").length, 1,
+        "There should be only one image request with a thumbnail displayed.");
+      is($(".requests-menu-icon[type=thumbnail]").src, TEST_IMAGE_DATA_URI,
+        "The image requests-menu-icon thumbnail is displayed correctly.");
+      is($(".requests-menu-icon[type=thumbnail]").hidden, false,
+        "The image requests-menu-icon thumbnail should not be hidden.");
+    }
+
+    aDebuggee.performRequests();
+  });
+}