diff --git a/browser/app/profile/firefox.js b/browser/app/profile/firefox.js
index 36d2166c482b..0b82c827a293 100644
--- a/browser/app/profile/firefox.js
+++ b/browser/app/profile/firefox.js
@@ -1820,4 +1820,9 @@ pref("print.enable_e10s_testing", false);
 pref("print.enable_e10s_testing", true);
 #endif
 
+#ifdef NIGHTLY_BUILD
+// Enable e10s add-on interposition by default.
+pref("extensions.interposition.enabled", true);
+#endif
+
 pref("browser.defaultbrowser.notificationbar", false);
diff --git a/toolkit/mozapps/extensions/internal/XPIProvider.jsm b/toolkit/mozapps/extensions/internal/XPIProvider.jsm
index 83711f9e0f98..46a88da2b13c 100644
--- a/toolkit/mozapps/extensions/internal/XPIProvider.jsm
+++ b/toolkit/mozapps/extensions/internal/XPIProvider.jsm
@@ -84,6 +84,7 @@ const PREF_INSTALL_REQUIREBUILTINCERTS = "extensions.install.requireBuiltInCerts
 const PREF_INSTALL_DISTRO_ADDONS      = "extensions.installDistroAddons";
 const PREF_BRANCH_INSTALLED_ADDON     = "extensions.installedDistroAddon.";
 const PREF_SHOWN_SELECTION_UI         = "extensions.shownSelectionUI";
+const PREF_INTERPOSITION_ENABLED      = "extensions.interposition.enabled";
 
 const PREF_EM_MIN_COMPAT_APP_VERSION      = "extensions.minCompatibleAppVersion";
 const PREF_EM_MIN_COMPAT_PLATFORM_VERSION = "extensions.minCompatiblePlatformVersion";
@@ -4282,13 +4283,11 @@ this.XPIProvider = {
 
     let principal = Cc["@mozilla.org/systemprincipal;1"].
                     createInstance(Ci.nsIPrincipal);
-#if defined(NIGHTLY_BUILD) && defined(HAVE_SHIMS)
-    if (!aMultiprocessCompatible) {
+    if (!aMultiprocessCompatible && Preferences.get(PREF_INTERPOSITION_ENABLED, false)) {
       let interposition = Cc["@mozilla.org/addons/multiprocess-shims;1"].
         getService(Ci.nsIAddonInterposition);
       Cu.setAddonInterposition(aId, interposition);
     }
-#endif
 
     if (!aFile.exists()) {
       this.bootstrapScopes[aId] =
diff --git a/toolkit/mozapps/extensions/internal/moz.build b/toolkit/mozapps/extensions/internal/moz.build
index 45b887335d32..24fe344bf7d2 100644
--- a/toolkit/mozapps/extensions/internal/moz.build
+++ b/toolkit/mozapps/extensions/internal/moz.build
@@ -14,9 +14,6 @@ EXTRA_JS_MODULES.addons += [
     'SpellCheckDictionaryBootstrap.js',
 ]
 
-if CONFIG['MOZ_BUILD_APP'] in ['browser']:
-      DEFINES['HAVE_SHIMS'] = True
-
 # Don't ship unused providers on Android
 if CONFIG['MOZ_WIDGET_TOOLKIT'] != 'android':
     EXTRA_JS_MODULES.addons += [
diff --git a/toolkit/xre/moz.build b/toolkit/xre/moz.build
index 3a81cd4e3ff1..85e38b4c0da7 100644
--- a/toolkit/xre/moz.build
+++ b/toolkit/xre/moz.build
@@ -105,9 +105,6 @@ if CONFIG['MOZ_UPDATER']:
 
 MSVC_ENABLE_PGO = True
 
-if CONFIG['MOZ_BUILD_APP'] in ['browser']:
-      DEFINES['HAVE_SHIMS'] = True
-
 include('/ipc/chromium/chromium-config.mozbuild')
 
 FINAL_LIBRARY = 'xul'
diff --git a/toolkit/xre/nsXREDirProvider.cpp b/toolkit/xre/nsXREDirProvider.cpp
index f290eea346f1..5deb4bc574ad 100644
--- a/toolkit/xre/nsXREDirProvider.cpp
+++ b/toolkit/xre/nsXREDirProvider.cpp
@@ -551,7 +551,9 @@ nsXREDirProvider::GetFiles(const char* aProperty, nsISimpleEnumerator** aResult)
 static void
 RegisterExtensionInterpositions(nsINIParser &parser)
 {
-#if defined(NIGHTLY_BUILD) && defined(HAVE_SHIMS)
+  if (!mozilla::Preferences::GetBool("extensions.interposition.enabled", false))
+    return;
+
   nsCOMPtr<nsIAddonInterposition> interposition =
     do_GetService("@mozilla.org/addons/multiprocess-shims;1");
 
@@ -570,7 +572,6 @@ RegisterExtensionInterpositions(nsINIParser &parser)
       continue;
   }
   while (true);
-#endif
 }
 
 static void