--- a/browser/components/loop/MozLoopService.jsm
+++ b/browser/components/loop/MozLoopService.jsm
@@ -4,16 +4,17 @@
 
 "use strict";
 
 const { classes: Cc, interfaces: Ci, utils: Cu } = Components;
 
 Cu.import("resource://gre/modules/Services.jsm");
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 Cu.import("resource://gre/modules/Promise.jsm");
+Cu.import("resource://gre/modules/osfile.jsm", this);
 
 this.EXPORTED_SYMBOLS = ["MozLoopService"];
 
 XPCOMUtils.defineLazyModuleGetter(this, "console",
   "resource://gre/modules/devtools/Console.jsm");
 
 XPCOMUtils.defineLazyModuleGetter(this, "injectLoopAPI",
   "resource:///modules/loop/MozLoopAPI.jsm");
@@ -47,17 +48,16 @@ XPCOMUtils.defineLazyServiceGetter(this,
  *
  * The registration is a two-part process. First we need to connect to
  * and register with the push server. Then we need to take the result of that
  * and register with the Loop server.
  */
 let MozLoopServiceInternal = {
   // The uri of the Loop server.
   loopServerUri: Services.prefs.getCharPref("loop.server"),
-  telemetryUri: Services.prefs.getCharPref("loop.telemetryURL"),
 
   // The current deferred for the registration process. This is set if in progress
   // or the registration was successful. This is null if a registration attempt was
   // unsuccessful.
   _registeredDeferred: null,
 
   /**
    * The initial delay for push registration. This ensures we don't start
@@ -309,75 +309,77 @@ let MozLoopServiceInternal = {
         map[key] = {};
       map[key][property] = string.value;
     }
 
     return this._localizedStrings = map;
   },
 
   /**
-   * Uploads telemetry logs to telemetryServer
+   * Saves loop logs to the saved-telemetry-pings folder.
    *
    * @param {Object} pc The peerConnection in question.
    */
-  uploadTelemetry: function(window, pc) {
-    if (!this.telemetryUri) {
-      return;
-    }
+  stageForTelemetryUpload: function(window, pc) {
     window.WebrtcGlobalInformation.getAllStats(allStats => {
       let internalFormat = allStats.reports[0]; // filtered on pc.id
       window.WebrtcGlobalInformation.getLogging('', logs => {
+        let report = convertToRTCStatsReport(internalFormat);
+        let logStr = "";
+        logs.forEach(s => { logStr += s + "\n"; });
 
         // We have stats and logs.
-        // Prepare payload from https://wiki.mozilla.org/Loop/Telemetry
+
+        // Create worker job. ping = saved telemetry ping file header + payload
+        //
+        // Prepare payload according to https://wiki.mozilla.org/Loop/Telemetry
 
         let ai = Services.appinfo;
-        let report = convertToRTCStatsReport(internalFormat);
-
-        let payload = {
-          ver: 1,
-          info: {
-            appUpdateChannel: ai.defaultUpdateChannel,
-            appBuildID: ai.appBuildID,
-            appName: ai.name,
-            appVersion: ai.version,
-            reason: "loop",
-            OS: ai.OS,
-            version: Services.sysinfo.getProperty("version")
-          },
-          report: "ice failure",
-          connectionstate: pc.iceConnectionState,
-          stats: report,
-          localSdp: internalFormat.localSdp,
-          remoteSdp: internalFormat.remoteSdp,
-          log: ""
-        };
-        logs.forEach(s => { payload.log += s + "\n"; });
-
         let uuid = uuidgen.generateUUID().toString();
         uuid = uuid.substr(1,uuid.length-2); // remove uuid curly braces
 
-        let url = this.telemetryUri;
-        url += ((url.substr(-1) == "/")? "":"/") + uuid + "/loop/" +
-                ai.OS + "/" + ai.version + "/" + ai.defaultUpdateChannel + "/" +
-                ai.appBuildID;
-
-        // Send payload.
-        //TODO: gzip!
-
-        let xhr = new window.XMLHttpRequest();
-        xhr.open("POST", url, true);
-        xhr.setRequestHeader("Content-Type", 'application/json');
-        xhr.onreadystatechange = function() {
-          if (xhr.readyState == 4 && xhr.status == 200) {
-            console.log("Failed to upload telemetry logs: " + xhr.responseText);
+        let directory = OS.Path.join(OS.Constants.Path.profileDir,
+                                     "saved-telemetry-pings");
+        let job = {
+          directory: directory,
+          filename: uuid + ".json",
+          ping: {
+            reason: "loop",
+            slug: uuid,
+            payload: {
+              ver: 1,
+              info: {
+                appUpdateChannel: ai.defaultUpdateChannel,
+                appBuildID: ai.appBuildID,
+                appName: ai.name,
+                appVersion: ai.version,
+                reason: "loop",
+                OS: ai.OS,
+                version: Services.sysinfo.getProperty("version")
+              },
+              report: "ice failure",
+              connectionstate: pc.iceConnectionState,
+              stats: report,
+              localSdp: internalFormat.localSdp,
+              remoteSdp: internalFormat.remoteSdp,
+              log: logStr
+            }
           }
         };
-        xhr.send(JSON.stringify(payload));
-        console.log("Uploading telemetry logs to " + url);
+
+        // Send job to worker to do saving to
+        // disk for pickup by telemetry on next startup, which then uploads it.
+
+        let worker = new ChromeWorker("MozLoopWorker.js");
+        worker.onmessage = function(e) {
+          console.log(e.data.ok ?
+            "Successfully staged loop report for telemetry upload." :
+            ("Failed to stage loop report. Error: " + e.data.fail));
+        }
+        worker.postMessage(job);
       });
     }, pc.id);
   },
 
   /**
    * Opens the chat window
    *
    * @param {Object} contentWindow The window to open the chat window in, may
@@ -415,17 +417,20 @@ let MozLoopServiceInternal = {
         let onPCLifecycleChange = (pc, winID, type) => {
           if (winID != ourID) {
             return;
           }
           if (type == "iceconnectionstatechange") {
             switch(pc.iceConnectionState) {
               case "failed":
               case "disconnected":
-                this.uploadTelemetry(window, pc);
+                if (Services.telemetry.canSend ||
+                    Services.prefs.getBoolPref("toolkit.telemetry.test")) {
+                  this.stageForTelemetryUpload(window, pc);
+                }
                 break;
             }
           }
         };
 
         let pc_static = new window.mozRTCPeerConnectionStatic();
         pc_static.registerPeerConnectionLifecycleCallback(onPCLifecycleChange);
       }.bind(this), true);

new file mode 100644
--- /dev/null
+++ b/browser/components/loop/MozLoopWorker.js
@@ -0,0 +1,54 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * A worker dedicated to loop-report sanitation and writing for MozLoopService.
+ */
+
+"use strict";
+
+importScripts("resource://gre/modules/osfile.jsm");
+
+let File = OS.File;
+let Encoder = new TextEncoder();
+let Counter = 0;
+
+const MAX_LOOP_LOGS = 5;
+/**
+ * Communications with the controller.
+ *
+ * Accepts messages:
+ * { path: filepath, ping: data }
+ *
+ * Sends messages:
+ * { ok: true }
+ * { fail: serialized_form_of_OS.File.Error }
+ */
+
+onmessage = function(e) {
+  if (++Counter > MAX_LOOP_LOGS) {
+    postMessage({
+      fail: "Maximum " + MAX_LOOP_LOGS + "loop reports reached for this session"
+    });
+    return;
+  }
+
+  let directory = e.data.directory;
+  let filename = e.data.filename;
+  let ping = e.data.ping;
+
+  let pingStr = JSON.stringify(ping);
+
+  // Save to disk
+  let array = Encoder.encode(pingStr);
+  try {
+    File.makeDir(directory,
+                 { unixMode: OS.Constants.S_IRWXU, ignoreExisting: true });
+    File.writeAtomic(OS.Path.join(directory, filename), array);
+    postMessage({ ok: true });
+  } catch (ex if ex instanceof File.Error) {
+    // Instances of OS.File.Error know how to serialize themselves
+    postMessage({fail: File.Error.toMsg(ex)});
+  }
+};

--- a/browser/components/loop/moz.build
+++ b/browser/components/loop/moz.build
@@ -9,9 +9,10 @@ JAR_MANIFESTS += ['jar.mn']
 JS_MODULES_PATH = 'modules/loop'
 
 XPCSHELL_TESTS_MANIFESTS += ['test/xpcshell/xpcshell.ini']
 
 EXTRA_JS_MODULES += [
     'MozLoopAPI.jsm',
     'MozLoopPushHandler.jsm',
     'MozLoopService.jsm',
+    'MozLoopWorker.js',
 ]