--- a/dom/tests/mochitest/general/test_interfaces.html
+++ b/dom/tests/mochitest/general/test_interfaces.html
@@ -543,17 +543,17 @@ var interfaceNamesInGlobalScope =
     "HTMLCollection",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "HTMLContentElement",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "HTMLDataElement",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "HTMLDataListElement",
 // IMPORTANT: Do not change this list without review from a DOM peer!
-    {name: "HTMLDetailsElement", release: false},
+    "HTMLDetailsElement",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "HTMLDirectoryElement",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "HTMLDivElement",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "HTMLDListElement",
 // IMPORTANT: Do not change this list without review from a DOM peer!
     "HTMLDocument",

--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -5224,23 +5224,17 @@ pref("narrate.voice", "automatic");
 // features, loading Gecko Media Plugins unsandboxed.  However, EME CDMs will not be
 // loaded without sandboxing even if this pref is changed.
 pref("media.gmp.insecure.allow", false);
 #endif
 
 pref("dom.audiochannel.mutedByDefault", false);
 
 // Enable <details> and <summary> tags.
-#ifdef RELEASE_BUILD
-// Bug 1226455: Need to modify dom/tests/mochitest/general/test_interfaces.html
-// when shipping.
-pref("dom.details_element.enabled", false);
-#else
 pref("dom.details_element.enabled", true);
-#endif
 
 // Secure Element API
 #ifdef MOZ_SECUREELEMENT
 pref("dom.secureelement.enabled", false);
 #endif
 
 // Allow control characters appear in composition string.
 // When this is false, control characters except