--- a/toolkit/components/telemetry/Histograms.json
+++ b/toolkit/components/telemetry/Histograms.json
@@ -2245,10 +2245,14 @@
   },
   "SOCIAL_TOGGLED": {
     "kind": "boolean",
     "description": "Social has been toggled to on or off"
   },
   "ENABLE_PRIVILEGE_EVER_CALLED": {
     "kind": "flag",
     "description": "Whether enablePrivilege has ever been called during the current session"
+  },
+  "READ_SAVED_PING_SUCCESS": {
+    "kind": "boolean",
+    "description": "Sucessful reading a saved ping file"
   }
 }

--- a/toolkit/components/telemetry/TelemetryPing.js
+++ b/toolkit/components/telemetry/TelemetryPing.js
@@ -715,35 +715,40 @@ TelemetryPing.prototype = {
       return true;
     }
 
     let checksumNow = this.hashString(ping.payload);
     return ping.checksum == checksumNow;
   },
 
   addToPendingPings: function addToPendingPings(file, stream) {
+    let success = false;
+
     try {
       let string = NetUtil.readInputStreamToString(stream, stream.available(), { charset: "UTF-8" });
       stream.close();
       let ping = JSON.parse(string);
       this._pingLoadsCompleted++;
 
       if (this.verifyPingChecksum(ping)) {
         this._pendingPings.push(ping);
       }
 
       if (this._doLoadSaveNotifications &&
           this._pingLoadsCompleted == this._pingsLoaded) {
         Services.obs.notifyObservers(null, "telemetry-test-load-complete", null);
       }
+      success = true;
     } catch (e) {
       // An error reading the file, or an error parsing the contents.
       stream.close();           // close is idempotent.
       file.remove(true);
     }
+    let success_histogram = Telemetry.getHistogramById("READ_SAVED_PING_SUCCESS");
+    success_histogram.add(success);
   },
 
   loadHistograms: function loadHistograms(file, sync) {
     this._pingsLoaded++;
     if (sync) {
       let stream = Cc["@mozilla.org/network/file-input-stream;1"]
                    .createInstance(Ci.nsIFileInputStream);
       stream.init(file, -1, -1, 0);

--- a/toolkit/components/telemetry/tests/unit/test_TelemetryPing.js
+++ b/toolkit/components/telemetry/tests/unit/test_TelemetryPing.js
@@ -185,17 +185,19 @@ function checkPayload(request, reason, s
   if (isWindows) {
     do_check_true(payload.simpleMeasurements.startupSessionRestoreReadBytes > 0);
     do_check_true(payload.simpleMeasurements.startupSessionRestoreWriteBytes > 0);
   }
 
   const TELEMETRY_PING = "TELEMETRY_PING";
   const TELEMETRY_SUCCESS = "TELEMETRY_SUCCESS";
   const TELEMETRY_TEST_FLAG = "TELEMETRY_TEST_FLAG";
+  const READ_SAVED_PING_SUCCESS = "READ_SAVED_PING_SUCCESS";
   do_check_true(TELEMETRY_PING in payload.histograms);
+  do_check_true(READ_SAVED_PING_SUCCESS in payload.histograms);
   let rh = Telemetry.registeredHistograms;
   for (let name in rh) {
     if (/SQLITE/.test(name) && name in payload.histograms) {
       do_check_true(("STARTUP_" + name) in payload.histograms); 
     }
   }
   do_check_false(IGNORE_HISTOGRAM in payload.histograms);
   do_check_false(IGNORE_CLONED_HISTOGRAM in payload.histograms);
@@ -217,16 +219,19 @@ function checkPayload(request, reason, s
     bucket_count: 3,
     histogram_type: 2,
     values: {0:1, 1:successfulPings, 2:0},
     sum: successfulPings
   };
   let tc = payload.histograms[TELEMETRY_SUCCESS];
   do_check_eq(uneval(tc), uneval(expected_tc));
 
+  let h = payload.histograms[READ_SAVED_PING_SUCCESS];
+  do_check_eq(h.values[0], 1);
+
   // The ping should include data from memory reporters.  We can't check that
   // this data is correct, because we can't control the values returned by the
   // memory reporters.  But we can at least check that the data is there.
   //
   // It's important to check for the presence of reporters with a mix of units,
   // because TelemetryPing has separate logic for each one.  But we can't
   // currently check UNITS_COUNT_CUMULATIVE or UNITS_PERCENTAGE because
   // Telemetry doesn't touch a memory reporter with these units that's