--- a/dom/workers/ServiceWorkerManager.cpp
+++ b/dom/workers/ServiceWorkerManager.cpp
@@ -31,16 +31,17 @@
 
 #include "mozilla/BasePrincipal.h"
 #include "mozilla/ClearOnShutdown.h"
 #include "mozilla/ErrorNames.h"
 #include "mozilla/LoadContext.h"
 #include "mozilla/Telemetry.h"
 #include "mozilla/dom/BindingUtils.h"
 #include "mozilla/dom/ContentParent.h"
+#include "mozilla/dom/ContentChild.h"
 #include "mozilla/dom/DOMError.h"
 #include "mozilla/dom/ErrorEvent.h"
 #include "mozilla/dom/Headers.h"
 #include "mozilla/dom/InternalHeaders.h"
 #include "mozilla/dom/Navigator.h"
 #include "mozilla/dom/NotificationEvent.h"
 #include "mozilla/dom/PromiseNativeHandler.h"
 #include "mozilla/dom/Request.h"
@@ -673,16 +674,27 @@ ServiceWorkerManager::Register(mozIDOMWi
     new ServiceWorkerRegisterJob(documentPrincipal, cleanedScope, spec,
                                  loadGroup, aLoadFlags);
   job->AppendResultCallback(cb);
   queue->ScheduleJob(job);
 
   AssertIsOnMainThread();
   Telemetry::Accumulate(Telemetry::SERVICE_WORKER_REGISTRATIONS, 1);
 
+  ContentChild* contentChild = ContentChild::GetSingleton();
+  if (contentChild &&
+      contentChild->GetRemoteType().EqualsLiteral(FILE_REMOTE_TYPE)) {
+    nsString message(NS_LITERAL_STRING("ServiceWorker registered by document "
+                                       "embedded in a file:/// URI.  This may "
+                                       "result in unexpected behavior."));
+    ReportToAllClients(cleanedScope, message, EmptyString(),
+                       EmptyString(), 0, 0, nsIScriptError::warningFlag);
+    Telemetry::Accumulate(Telemetry::FILE_EMBEDDED_SERVICEWORKERS, 1);
+  }
+
   promise.forget(aPromise);
   return NS_OK;
 }
 
 void
 ServiceWorkerManager::AppendPendingOperation(nsIRunnable* aRunnable)
 {
   MOZ_ASSERT(!mActor);

--- a/toolkit/components/telemetry/Histograms.json
+++ b/toolkit/components/telemetry/Histograms.json
@@ -9626,16 +9626,23 @@
   },
   "SERVICE_WORKER_LIFE_TIME": {
     "expires_in_version": "50",
     "kind": "exponential",
     "high": 120000,
     "n_buckets": 20,
     "description": "Tracking how long a ServiceWorker stays alive after it is spawned. File bugs in Core::DOM in case of a Telemetry regression."
   },
+  "FILE_EMBEDDED_SERVICEWORKERS": {
+    "alert_emails": ["dparks@mozilla.com"],
+    "expires_in_version": "58",
+    "kind": "count",
+    "bug_numbers": [1312788],
+    "description": "Count ServiceWorkers that are embedded in pages loading with the file:/// protocol."
+  },
   "GRAPHICS_SANITY_TEST": {
     "expires_in_version": "never",
     "alert_emails": ["gfx-telemetry-alerts@mozilla.com","msreckovic@mozilla.com"],
     "kind": "enumerated",
     "n_values": 20,
     "releaseChannelCollection": "opt-out",
     "description": "Reports results from the graphics sanity test to track which drivers are having problems (0=TEST_PASSED, 1=TEST_FAILED_RENDER, 2=TEST_FAILED_VIDEO, 3=TEST_CRASHED)"
   },