diff --git a/dom/tests/mochitest/general/test_interfaces.html b/dom/tests/mochitest/general/test_interfaces.html
index f9dc582b4e49..21ad5985a526 100644
--- a/dom/tests/mochitest/general/test_interfaces.html
+++ b/dom/tests/mochitest/general/test_interfaces.html
@@ -923,7 +923,7 @@ var interfaceNamesInGlobalScope =
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "SettingsManager",
 // IMPORTANT: Do not change this list without review from a DOM peer!
-    {name: "ShadowRoot", pref: "dom.webcomponents.enabled"},
+    "ShadowRoot", // Bogus, but the test harness forces it on.  See bug 1159768.
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "SharedWorker",
 // IMPORTANT: Do not change this list without review from a DOM peer!
@@ -1381,7 +1381,6 @@ var interfaceNamesInGlobalScope =
 // IMPORTANT: Do not change the list above without review from a DOM peer!
 
 function createInterfaceMap(isXBLScope) {
-  var prefs = SpecialPowers.Services.prefs;
   var version = SpecialPowers.Cc["@mozilla.org/xre/app-info;1"].getService(SpecialPowers.Ci.nsIXULAppInfo).version;
   var isNightly = version.endsWith("a1");
   var isRelease = !version.includes("a");
@@ -1406,21 +1405,23 @@ function createInterfaceMap(isXBLScope) {
     for (var entry of interfaces) {
       if (typeof(entry) === "string") {
         interfaceMap[entry] = true;
-      } else if ((entry.nightly === !isNightly) ||
-                 (entry.xbl === !isXBLScope) ||
-                 (entry.desktop === !isDesktop) ||
-                 (entry.b2g === !isB2G) ||
-                 (entry.windows === !isWindows) ||
-                 (entry.mac === !isMac) ||
-                 (entry.linux === !isLinux) ||
-                 (entry.android === !isAndroid) ||
-                 (entry.release === !isRelease) ||
-                 (entry.pref && !prefs.getBoolPref(entry.pref))  ||
-                 (entry.permission && !hasPermission(entry.permission)) ||
-                 entry.disabled) {
-        interfaceMap[entry.name] = false;
       } else {
-        interfaceMap[entry.name] = true;
+	ok(!("pref" in entry), "Bogus pref annotation for " + entry.name);
+	if ((entry.nightly === !isNightly) ||
+            (entry.xbl === !isXBLScope) ||
+            (entry.desktop === !isDesktop) ||
+            (entry.b2g === !isB2G) ||
+            (entry.windows === !isWindows) ||
+            (entry.mac === !isMac) ||
+            (entry.linux === !isLinux) ||
+            (entry.android === !isAndroid) ||
+            (entry.release === !isRelease) ||
+            (entry.permission && !hasPermission(entry.permission)) ||
+            entry.disabled) {
+          interfaceMap[entry.name] = false;
+	} else {
+          interfaceMap[entry.name] = true;
+	}
       }
     }
   }
diff --git a/dom/workers/test/serviceworkers/test_serviceworker_interfaces.js b/dom/workers/test/serviceworkers/test_serviceworker_interfaces.js
index 92aeeba4d1c9..13caa0baf8a8 100644
--- a/dom/workers/test/serviceworkers/test_serviceworker_interfaces.js
+++ b/dom/workers/test/serviceworkers/test_serviceworker_interfaces.js
@@ -192,7 +192,7 @@ var interfaceNamesInGlobalScope =
   ];
 // IMPORTANT: Do not change the list above without review from a DOM peer!
 
-function createInterfaceMap(prefMap, permissionMap, version, userAgent, isB2G) {
+function createInterfaceMap(permissionMap, version, userAgent, isB2G) {
   var isNightly = version.endsWith("a1");
   var isRelease = !version.includes("a");
   var isDesktop = !/Mobile|Tablet/.test(userAgent);
@@ -205,16 +205,18 @@ function createInterfaceMap(prefMap, permissionMap, version, userAgent, isB2G) {
     for (var entry of interfaces) {
       if (typeof(entry) === "string") {
         interfaceMap[entry] = true;
-      } else if ((entry.nightly === !isNightly) ||
-                 (entry.desktop === !isDesktop) ||
-                 (entry.android === !isAndroid) ||
-                 (entry.b2g === !isB2G) ||
-                 (entry.release === !isRelease) ||
-                 (entry.pref && !prefMap[entry.pref])  ||
-                 (entry.permission && !permissionMap[entry.permission])) {
-        interfaceMap[entry.name] = false;
       } else {
-        interfaceMap[entry.name] = true;
+        ok(!("pref" in entry), "Bogus pref annotation for " + entry.name);
+        if ((entry.nightly === !isNightly) ||
+            (entry.desktop === !isDesktop) ||
+            (entry.android === !isAndroid) ||
+            (entry.b2g === !isB2G) ||
+            (entry.release === !isRelease) ||
+            (entry.permission && !permissionMap[entry.permission])) {
+          interfaceMap[entry.name] = false;
+        } else {
+          interfaceMap[entry.name] = true;
+        }
       }
     }
   }
@@ -225,8 +227,8 @@ function createInterfaceMap(prefMap, permissionMap, version, userAgent, isB2G) {
   return interfaceMap;
 }
 
-function runTest(prefMap, permissionMap, version, userAgent, isB2G) {
-  var interfaceMap = createInterfaceMap(prefMap, permissionMap, version, userAgent, isB2G);
+function runTest(permissionMap, version, userAgent, isB2G) {
+  var interfaceMap = createInterfaceMap(permissionMap, version, userAgent, isB2G);
   for (var name of Object.getOwnPropertyNames(self)) {
     // An interface name should start with an upper case character.
     if (!/^[A-Z]/.test(name)) {
@@ -249,18 +251,6 @@ function runTest(prefMap, permissionMap, version, userAgent, isB2G) {
      "The following interface(s) are not enumerated: " + Object.keys(interfaceMap).join(", "));
 }
 
-function appendPrefs(prefs, interfaces) {
-  for (var entry of interfaces) {
-    if (entry.pref !== undefined && prefs.indexOf(entry.pref) === -1) {
-      prefs.push(entry.pref);
-    }
-  }
-}
-
-var prefs = [];
-appendPrefs(prefs, ecmaGlobals);
-appendPrefs(prefs, interfaceNamesInGlobalScope);
-
 function appendPermissions(permissions, interfaces) {
   for (var entry of interfaces) {
     if (entry.permission !== undefined &&
@@ -274,14 +264,12 @@ var permissions = [];
 appendPermissions(permissions, ecmaGlobals);
 appendPermissions(permissions, interfaceNamesInGlobalScope);
 
-workerTestGetPrefs(prefs, function(prefMap) {
-  workerTestGetPermissions(permissions, function(permissionMap) {
-    workerTestGetVersion(function(version) {
-      workerTestGetUserAgent(function(userAgent) {
-        workerTestGetIsB2G(function(isB2G) {
-          runTest(prefMap, permissionMap, version, userAgent, isB2G);
-          workerTestDone();
-	});
+workerTestGetPermissions(permissions, function(permissionMap) {
+  workerTestGetVersion(function(version) {
+    workerTestGetUserAgent(function(userAgent) {
+      workerTestGetIsB2G(function(isB2G) {
+        runTest(permissionMap, version, userAgent, isB2G);
+        workerTestDone();
       });
     });
   });
diff --git a/dom/workers/test/test_worker_interfaces.js b/dom/workers/test/test_worker_interfaces.js
index e7aa419a45c1..01aebda8db89 100644
--- a/dom/workers/test/test_worker_interfaces.js
+++ b/dom/workers/test/test_worker_interfaces.js
@@ -180,7 +180,7 @@ var interfaceNamesInGlobalScope =
   ];
 // IMPORTANT: Do not change the list above without review from a DOM peer!
 
-function createInterfaceMap(prefMap, permissionMap, version, userAgent, isB2G) {
+function createInterfaceMap(permissionMap, version, userAgent, isB2G) {
   var isNightly = version.endsWith("a1");
   var isRelease = !version.includes("a");
   var isDesktop = !/Mobile|Tablet/.test(userAgent);
@@ -193,17 +193,19 @@ function createInterfaceMap(prefMap, permissionMap, version, userAgent, isB2G) {
     for (var entry of interfaces) {
       if (typeof(entry) === "string") {
         interfaceMap[entry] = true;
-      } else if ((entry.nightly === !isNightly) ||
-                 (entry.desktop === !isDesktop) ||
-                 (entry.android === !isAndroid) ||
-                 (entry.b2g === !isB2G) ||
-                 (entry.release === !isRelease) ||
-                 (entry.pref && !prefMap[entry.pref])  ||
-                 (entry.permission && !permissionMap[entry.permission]) ||
-                 entry.disabled) {
-        interfaceMap[entry.name] = false;
       } else {
-        interfaceMap[entry.name] = true;
+        ok(!("pref" in entry), "Bogus pref annotation for " + entry.name);
+        if ((entry.nightly === !isNightly) ||
+            (entry.desktop === !isDesktop) ||
+            (entry.android === !isAndroid) ||
+            (entry.b2g === !isB2G) ||
+            (entry.release === !isRelease) ||
+            (entry.permission && !permissionMap[entry.permission]) ||
+            entry.disabled) {
+          interfaceMap[entry.name] = false;
+        } else {
+          interfaceMap[entry.name] = true;
+        }
       }
     }
   }
@@ -214,8 +216,8 @@ function createInterfaceMap(prefMap, permissionMap, version, userAgent, isB2G) {
   return interfaceMap;
 }
 
-function runTest(prefMap, permissionMap, version, userAgent, isB2G) {
-  var interfaceMap = createInterfaceMap(prefMap, permissionMap, version, userAgent, isB2G);
+function runTest(permissionMap, version, userAgent, isB2G) {
+  var interfaceMap = createInterfaceMap(permissionMap, version, userAgent, isB2G);
   for (var name of Object.getOwnPropertyNames(self)) {
     // An interface name should start with an upper case character.
     if (!/^[A-Z]/.test(name)) {
@@ -238,18 +240,6 @@ function runTest(prefMap, permissionMap, version, userAgent, isB2G) {
      "The following interface(s) are not enumerated: " + Object.keys(interfaceMap).join(", "));
 }
 
-function appendPrefs(prefs, interfaces) {
-  for (var entry of interfaces) {
-    if (entry.pref !== undefined && prefs.indexOf(entry.pref) === -1) {
-      prefs.push(entry.pref);
-    }
-  }
-}
-
-var prefs = [];
-appendPrefs(prefs, ecmaGlobals);
-appendPrefs(prefs, interfaceNamesInGlobalScope);
-
 function appendPermissions(permissions, interfaces) {
   for (var entry of interfaces) {
     if (entry.permission !== undefined &&
@@ -263,14 +253,12 @@ var permissions = [];
 appendPermissions(permissions, ecmaGlobals);
 appendPermissions(permissions, interfaceNamesInGlobalScope);
 
-workerTestGetPrefs(prefs, function(prefMap) {
-  workerTestGetPermissions(permissions, function(permissionMap) {
-    workerTestGetVersion(function(version) {
-      workerTestGetUserAgent(function(userAgent) {
-        workerTestGetIsB2G(function(isB2G) {
-          runTest(prefMap, permissionMap, version, userAgent, isB2G);
-          workerTestDone();
-	});
+workerTestGetPermissions(permissions, function(permissionMap) {
+  workerTestGetVersion(function(version) {
+    workerTestGetUserAgent(function(userAgent) {
+      workerTestGetIsB2G(function(isB2G) {
+        runTest(permissionMap, version, userAgent, isB2G);
+        workerTestDone();
       });
     });
   });