--- a/dom/workers/RuntimeService.cpp
+++ b/dom/workers/RuntimeService.cpp
@@ -160,16 +160,17 @@ static_assert(MAX_WORKERS_PER_DOMAIN >= 
 #define PREF_DOM_CACHES_ENABLED        "dom.caches.enabled"
 #define PREF_DOM_CACHES_TESTING_ENABLED "dom.caches.testing.enabled"
 #define PREF_DOM_WORKERNOTIFICATION_ENABLED  "dom.webnotifications.enabled"
 #define PREF_WORKERS_LATEST_JS_VERSION "dom.workers.latestJSVersion"
 #define PREF_INTL_ACCEPT_LANGUAGES     "intl.accept_languages"
 #define PREF_SERVICEWORKERS_ENABLED    "dom.serviceWorkers.enabled"
 #define PREF_SERVICEWORKERS_TESTING_ENABLED "dom.serviceWorkers.testing.enabled"
 #define PREF_INTERCEPTION_ENABLED      "dom.serviceWorkers.interception.enabled"
+#define PREF_INTERCEPTION_OPAQUE_ENABLED "dom.serviceWorkers.interception.opaque.enabled"
 
 namespace {
 
 const uint32_t kNoIndex = uint32_t(-1);
 
 const JS::ContextOptions kRequiredContextOptions =
   JS::ContextOptions().setDontReportUncaught(true);
 
@@ -1929,16 +1930,20 @@ RuntimeService::Init()
                                   PREF_SERVICEWORKERS_ENABLED,
                                   reinterpret_cast<void *>(WORKERPREF_SERVICEWORKERS))) ||
       NS_FAILED(Preferences::RegisterCallbackAndCall(
                                   WorkerPrefChanged,
                                   PREF_INTERCEPTION_ENABLED,
                                   reinterpret_cast<void *>(WORKERPREF_INTERCEPTION_ENABLED))) ||
       NS_FAILED(Preferences::RegisterCallbackAndCall(
                                   WorkerPrefChanged,
+                                  PREF_INTERCEPTION_OPAQUE_ENABLED,
+                                  reinterpret_cast<void *>(WORKERPREF_INTERCEPTION_OPAQUE_ENABLED))) ||
+      NS_FAILED(Preferences::RegisterCallbackAndCall(
+                                  WorkerPrefChanged,
                                   PREF_DOM_CACHES_TESTING_ENABLED,
                                   reinterpret_cast<void *>(WORKERPREF_DOM_CACHES_TESTING))) ||
       NS_FAILED(Preferences::RegisterCallbackAndCall(
                                   WorkerPrefChanged,
                                   PREF_SERVICEWORKERS_TESTING_ENABLED,
                                   reinterpret_cast<void *>(WORKERPREF_SERVICEWORKERS_TESTING))) ||
       NS_FAILED(Preferences::RegisterCallback(LoadRuntimeOptions,
                                               PREF_JS_OPTIONS_PREFIX,
@@ -2140,16 +2145,20 @@ RuntimeService::Cleanup()
                                   PREF_SERVICEWORKERS_TESTING_ENABLED,
                                   reinterpret_cast<void *>(WORKERPREF_SERVICEWORKERS_TESTING))) ||
         NS_FAILED(Preferences::UnregisterCallback(
                                   WorkerPrefChanged,
                                   PREF_DOM_CACHES_TESTING_ENABLED,
                                   reinterpret_cast<void *>(WORKERPREF_DOM_CACHES_TESTING))) ||
         NS_FAILED(Preferences::UnregisterCallback(
                                   WorkerPrefChanged,
+                                  PREF_INTERCEPTION_OPAQUE_ENABLED,
+                                  reinterpret_cast<void *>(WORKERPREF_INTERCEPTION_OPAQUE_ENABLED))) ||
+        NS_FAILED(Preferences::UnregisterCallback(
+                                  WorkerPrefChanged,
                                   PREF_INTERCEPTION_ENABLED,
                                   reinterpret_cast<void *>(WORKERPREF_INTERCEPTION_ENABLED))) ||
         NS_FAILED(Preferences::UnregisterCallback(
                                   WorkerPrefChanged,
                                   PREF_SERVICEWORKERS_ENABLED,
                                   reinterpret_cast<void *>(WORKERPREF_SERVICEWORKERS))) ||
         NS_FAILED(Preferences::UnregisterCallback(
                                   WorkerPrefChanged,
@@ -2699,16 +2708,17 @@ RuntimeService::WorkerPrefChanged(const 
   switch (key) {
     case WORKERPREF_DOM_CACHES:
     case WORKERPREF_DOM_CACHES_TESTING:
     case WORKERPREF_DOM_WORKERNOTIFICATION:
 #ifdef DUMP_CONTROLLED_BY_PREF
     case WORKERPREF_DUMP:
 #endif
     case WORKERPREF_INTERCEPTION_ENABLED:
+    case WORKERPREF_INTERCEPTION_OPAQUE_ENABLED:
     case WORKERPREF_SERVICEWORKERS:
     case WORKERPREF_SERVICEWORKERS_TESTING:
       sDefaultPreferences[key] = Preferences::GetBool(aPrefName, false);
       break;
 
     default:
       MOZ_ASSERT_UNREACHABLE("Invalid pref key");
       break;

--- a/dom/workers/WorkerPrivate.h
+++ b/dom/workers/WorkerPrivate.h
@@ -1287,16 +1287,23 @@ public:
   bool
   InterceptionEnabled() const
   {
     AssertIsOnWorkerThread();
     return mPreferences[WORKERPREF_INTERCEPTION_ENABLED];
   }
 
   bool
+  OpaqueInterceptionEnabled() const
+  {
+    AssertIsOnWorkerThread();
+    return mPreferences[WORKERPREF_INTERCEPTION_OPAQUE_ENABLED];
+  }
+
+  bool
   DOMWorkerNotificationEnabled() const
   {
     AssertIsOnWorkerThread();
     return mPreferences[WORKERPREF_DOM_WORKERNOTIFICATION];
   }
 
   bool
   DOMCachesTestingEnabled() const

--- a/dom/workers/Workers.h
+++ b/dom/workers/Workers.h
@@ -197,16 +197,17 @@ enum WorkerPreference
 {
   WORKERPREF_DUMP = 0, // browser.dom.window.dump.enabled
   WORKERPREF_DOM_CACHES, // dom.caches.enabled
   WORKERPREF_SERVICEWORKERS, // dom.serviceWorkers.enabled
   WORKERPREF_INTERCEPTION_ENABLED, // dom.serviceWorkers.interception.enabled
   WORKERPREF_DOM_WORKERNOTIFICATION, // dom.webnotifications.workers.enabled
   WORKERPREF_DOM_CACHES_TESTING, // dom.caches.testing.enabled
   WORKERPREF_SERVICEWORKERS_TESTING, // dom.serviceWorkers.testing.enabled
+  WORKERPREF_INTERCEPTION_OPAQUE_ENABLED, // dom.serviceWorkers.interception.opaque.enabled
   WORKERPREF_COUNT
 };
 
 // Implemented in WorkerPrivate.cpp
 
 struct WorkerLoadInfo
 {
   // All of these should be released in WorkerPrivateParent::ForgetMainThreadObjects.

--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -130,16 +130,22 @@ pref("dom.workers.enabled", true);
 pref("dom.workers.maxPerDomain", 20);
 
 // Whether or not Shared Web Workers are enabled.
 pref("dom.workers.sharedWorkers.enabled", true);
 
 // Service workers
 pref("dom.serviceWorkers.enabled", false);
 
+// Allow service workers to intercept network requests using the fetch event
+pref("dom.serviceWorkers.interception.enabled", false);
+
+// Allow service workers to intercept opaque (cross origin) responses
+pref("dom.serviceWorkers.interception.opaque.enabled", false);
+
 // Whether nonzero values can be returned from performance.timing.*
 pref("dom.enable_performance", true);
 
 // Whether resource timing will be gathered and returned by performance.GetEntries*
 pref("dom.enable_resource_timing", true);
 
 // Enable high-resolution timing markers for users
 pref("dom.enable_user_timing", true);