diff --git a/devtools/client/preferences/devtools.js b/devtools/client/preferences/devtools.js
index 788d4667b..2aa1f37a4 100644
--- a/devtools/client/preferences/devtools.js
+++ b/devtools/client/preferences/devtools.js
@@ -108,11 +108,7 @@ pref("devtools.debugger.auto-pretty-print", false);
 pref("devtools.debugger.auto-black-box", true);
 pref("devtools.debugger.workers", false);
 
-#ifdef RELEASE_OR_BETA
 pref("devtools.debugger.new-debugger-frontend", false);
-#else
-pref("devtools.debugger.new-debugger-frontend", true);
-#endif
 
 // The default Debugger UI settings
 pref("devtools.debugger.ui.panes-workers-and-sources-width", 200);
diff --git a/dom/base/nsDOMClassInfo.cpp b/dom/base/nsDOMClassInfo.cpp
index 068c8b0c5..681af8d0b 100644
--- a/dom/base/nsDOMClassInfo.cpp
+++ b/dom/base/nsDOMClassInfo.cpp
@@ -1607,9 +1607,7 @@ nsWindowSH::NameStructEnabled(JSContext* aCx, nsGlobalWindow *aWin,
          OldBindingConstructorEnabled(nameStruct, aWin, aCx);
 }
 
-#ifdef RELEASE_OR_BETA
 #define USE_CONTROLLERS_SHIM
-#endif
 
 #ifdef USE_CONTROLLERS_SHIM
 static const JSClass ControllersShimClass = {
diff --git a/dom/cache/CacheWorkerHolder.cpp b/dom/cache/CacheWorkerHolder.cpp
index 3879e1521..526a37233 100644
--- a/dom/cache/CacheWorkerHolder.cpp
+++ b/dom/cache/CacheWorkerHolder.cpp
@@ -55,11 +55,7 @@ CacheWorkerHolder::RemoveActor(ActorChild* aActor)
   NS_ASSERT_OWNINGTHREAD(CacheWorkerHolder);
   MOZ_DIAGNOSTIC_ASSERT(aActor);
 
-#if defined(RELEASE_OR_BETA)
   mActorList.RemoveElement(aActor);
-#else
-  MOZ_DIAGNOSTIC_ASSERT(mActorList.RemoveElement(aActor));
-#endif
 
   MOZ_ASSERT(!mActorList.Contains(aActor));
 }
diff --git a/dom/cache/DBSchema.cpp b/dom/cache/DBSchema.cpp
index 54b37feed..4e1fbf593 100644
--- a/dom/cache/DBSchema.cpp
+++ b/dom/cache/DBSchema.cpp
@@ -2554,12 +2554,14 @@ Migrate(mozIStorageConnection* aConn)
       }
     }
 
-#if defined(DEBUG) || !defined(RELEASE_OR_BETA)
+#if defined(DEBUG)
     int32_t lastVersion = currentVersion;
 #endif
     rv = aConn->GetSchemaVersion(&currentVersion);
     if (NS_WARN_IF(NS_FAILED(rv))) { return rv; }
+#if defined(DEBUG)
     MOZ_DIAGNOSTIC_ASSERT(currentVersion > lastVersion);
+#endif
   }
 
   // Don't release assert this since people do sometimes share profiles
diff --git a/dom/cache/Manager.cpp b/dom/cache/Manager.cpp
index 8d2835093..be3f05ad8 100644
--- a/dom/cache/Manager.cpp
+++ b/dom/cache/Manager.cpp
@@ -1531,11 +1531,13 @@ Manager::ReleaseCacheId(CacheId aCacheId)
   NS_ASSERT_OWNINGTHREAD(Manager);
   for (uint32_t i = 0; i < mCacheIdRefs.Length(); ++i) {
     if (mCacheIdRefs[i].mCacheId == aCacheId) {
-#if defined(DEBUG) || !defined(RELEASE_OR_BETA)
+#if defined(DEBUG)
       uint32_t oldRef = mCacheIdRefs[i].mCount;
 #endif
       mCacheIdRefs[i].mCount -= 1;
+#if defined(DEBUG)
       MOZ_DIAGNOSTIC_ASSERT(mCacheIdRefs[i].mCount < oldRef);
+#endif
       if (mCacheIdRefs[i].mCount == 0) {
         bool orphaned = mCacheIdRefs[i].mOrphaned;
         mCacheIdRefs.RemoveElementAt(i);
@@ -1582,11 +1584,13 @@ Manager::ReleaseBodyId(const nsID& aBodyId)
   NS_ASSERT_OWNINGTHREAD(Manager);
   for (uint32_t i = 0; i < mBodyIdRefs.Length(); ++i) {
     if (mBodyIdRefs[i].mBodyId == aBodyId) {
-#if defined(DEBUG) || !defined(RELEASE_OR_BETA)
+#if defined(DEBUG)
       uint32_t oldRef = mBodyIdRefs[i].mCount;
 #endif
       mBodyIdRefs[i].mCount -= 1;
+#if defined(DEBUG)
       MOZ_DIAGNOSTIC_ASSERT(mBodyIdRefs[i].mCount < oldRef);
+#endif
       if (mBodyIdRefs[i].mCount < 1) {
         bool orphaned = mBodyIdRefs[i].mOrphaned;
         mBodyIdRefs.RemoveElementAt(i);
diff --git a/dom/cache/ReadStream.cpp b/dom/cache/ReadStream.cpp
index efce027a1..f28556cd4 100644
--- a/dom/cache/ReadStream.cpp
+++ b/dom/cache/ReadStream.cpp
@@ -490,12 +490,6 @@ ReadStream::Create(const CacheReadStream& aReadStream)
   nsCOMPtr<nsIInputStream> stream = DeserializeIPCStream(aReadStream.stream());
   MOZ_DIAGNOSTIC_ASSERT(stream);
 
-  // Currently we expect all cache read streams to be blocking file streams.
-#if !defined(RELEASE_OR_BETA)
-  nsCOMPtr<nsIAsyncInputStream> asyncStream = do_QueryInterface(stream);
-  MOZ_DIAGNOSTIC_ASSERT(!asyncStream);
-#endif
-
   RefPtr<Inner> inner = new Inner(control, aReadStream.id(), stream);
   RefPtr<ReadStream> ref = new ReadStream(inner);
   return ref.forget();
diff --git a/dom/cache/StreamControl.cpp b/dom/cache/StreamControl.cpp
index 69a72d0b6..7a32d5634 100644
--- a/dom/cache/StreamControl.cpp
+++ b/dom/cache/StreamControl.cpp
@@ -45,7 +45,7 @@ void
 StreamControl::CloseReadStreams(const nsID& aId)
 {
   AssertOwningThread();
-#if defined(DEBUG) || !defined(RELEASE_OR_BETA)
+#if defined(DEBUG)
   uint32_t closedCount = 0;
 #endif
 
@@ -54,13 +54,15 @@ StreamControl::CloseReadStreams(const nsID& aId)
     RefPtr<ReadStream::Controllable> stream = iter.GetNext();
     if (stream->MatchId(aId)) {
       stream->CloseStream();
-#if defined(DEBUG) || !defined(RELEASE_OR_BETA)
+#if defined(DEBUG)
       closedCount += 1;
 #endif
     }
   }
 
+#if defined(DEBUG)
   MOZ_DIAGNOSTIC_ASSERT(closedCount > 0);
+#endif
 }
 
 void
diff --git a/dom/plugins/base/nsPluginTags.cpp b/dom/plugins/base/nsPluginTags.cpp
index ddc3968fd..3a80fdb6e 100644
--- a/dom/plugins/base/nsPluginTags.cpp
+++ b/dom/plugins/base/nsPluginTags.cpp
@@ -375,10 +375,10 @@ void nsPluginTag::InitMime(const char* const* aMimeTypes,
         break;
       case nsPluginHost::eSpecialType_None:
       default:
-#ifndef RELEASE_OR_BETA
-        // Allow async init for all plugins on Nightly and Aurora
-        mSupportsAsyncInit = true;
-#endif
+        // XXXMC: Async init for all plugins is experimental, but was historically
+        // default-enabled here on Nightly and Aurora but not release.
+        // Likely not a big concern. We can wait for plugins to be ready.
+        mSupportsAsyncInit = false;
         break;
     }
 
diff --git a/dom/worklet/Worklet.cpp b/dom/worklet/Worklet.cpp
index cb75a545b..0f07efa47 100644
--- a/dom/worklet/Worklet.cpp
+++ b/dom/worklet/Worklet.cpp
@@ -333,9 +333,8 @@ Worklet::Worklet(nsPIDOMWindowInner* aWindow, nsIPrincipal* aPrincipal,
   MOZ_ASSERT(aWindow);
   MOZ_ASSERT(aPrincipal);
 
-#ifdef RELEASE_OR_BETA
+  // XXXMC: Do we want this worklet code in the future?
   MOZ_CRASH("This code should not go to release/beta yet!");
-#endif
 }
 
 Worklet::~Worklet()
diff --git a/gfx/thebes/gfxFont.cpp b/gfx/thebes/gfxFont.cpp
index 808805875..6ad1a0012 100644
--- a/gfx/thebes/gfxFont.cpp
+++ b/gfx/thebes/gfxFont.cpp
@@ -175,7 +175,7 @@ gfxFontCache::gfxFontCache()
         obs->AddObserver(new Observer, "memory-pressure", false);
     }
 
-#ifndef RELEASE_OR_BETA
+#if 0
     // Currently disabled for release builds, due to unexplained crashes
     // during expiration; see bug 717175 & 894798.
     mWordCacheExpirationTimer = do_CreateInstance("@mozilla.org/timer;1");
@@ -2579,22 +2579,12 @@ gfxFont::GetShapedWord(DrawTarget *aDrawTarget,
         Telemetry::Accumulate((isContent ? Telemetry::WORD_CACHE_HITS_CONTENT :
                                    Telemetry::WORD_CACHE_HITS_CHROME),
                               aLength);
-#ifndef RELEASE_OR_BETA
-        if (aTextPerf) {
-            aTextPerf->current.wordCacheHit++;
-        }
-#endif
         return sw;
     }
 
     Telemetry::Accumulate((isContent ? Telemetry::WORD_CACHE_MISSES_CONTENT :
                                Telemetry::WORD_CACHE_MISSES_CHROME),
                           aLength);
-#ifndef RELEASE_OR_BETA
-    if (aTextPerf) {
-        aTextPerf->current.wordCacheMiss++;
-    }
-#endif
 
     sw = gfxShapedWord::Create(aText, aLength, aRunScript, aAppUnitsPerDevUnit,
                                aFlags);
@@ -2856,7 +2846,7 @@ gfxFont::ShapeTextWithoutWordCache(DrawTarget *aDrawTarget,
     return ok;
 }
 
-#ifndef RELEASE_OR_BETA
+#ifdef DEBUG
 #define TEXT_PERF_INCR(tp, m) (tp ? (tp)->current.m++ : 0)
 #else
 #define TEXT_PERF_INCR(tp, m)
@@ -2896,7 +2886,7 @@ gfxFont::SplitAndInitTextRun(DrawTarget *aDrawTarget,
 
     gfxTextPerfMetrics *tp = nullptr;
 
-#ifndef RELEASE_OR_BETA
+#ifdef DEBUG
     tp = aTextRun->GetFontGroup()->GetTextPerfMetrics();
     if (tp) {
         if (mStyle.systemFont) {
diff --git a/gfx/thebes/gfxPrefs.h b/gfx/thebes/gfxPrefs.h
index 8544c68e0..5baae6078 100644
--- a/gfx/thebes/gfxPrefs.h
+++ b/gfx/thebes/gfxPrefs.h
@@ -355,12 +355,9 @@ private:
 #if defined(ANDROID)
   DECL_GFX_PREF(Once, "gfx.apitrace.enabled",                  UseApitrace, bool, false);
 #endif
-#if defined(RELEASE_OR_BETA)
-  // "Skip" means this is locked to the default value in beta and release.
-  DECL_GFX_PREF(Skip, "gfx.blocklist.all",                     BlocklistAll, int32_t, 0);
-#else
+  // Tweaking/debug pref: -1 = ignore active blocklist entry, 0 = normal, 1 = block all features
   DECL_GFX_PREF(Once, "gfx.blocklist.all",                     BlocklistAll, int32_t, 0);
-#endif
+
   DECL_GFX_PREF(Live, "gfx.canvas.auto_accelerate.min_calls",  CanvasAutoAccelerateMinCalls, int32_t, 4);
   DECL_GFX_PREF(Live, "gfx.canvas.auto_accelerate.min_frames", CanvasAutoAccelerateMinFrames, int32_t, 30);
   DECL_GFX_PREF(Live, "gfx.canvas.auto_accelerate.min_seconds", CanvasAutoAccelerateMinSeconds, float, 5.0f);
diff --git a/gfx/thebes/gfxTextRun.cpp b/gfx/thebes/gfxTextRun.cpp
index c33589fa3..e7590131d 100644
--- a/gfx/thebes/gfxTextRun.cpp
+++ b/gfx/thebes/gfxTextRun.cpp
@@ -152,7 +152,7 @@ gfxTextRun::gfxTextRun(const gfxTextRunFactory::Parameters *aParams,
     NS_ASSERTION(mAppUnitsPerDevUnit > 0, "Invalid app unit scale");
     NS_ADDREF(mFontGroup);
 
-#ifndef RELEASE_OR_BETA
+#ifdef DEBUG
     gfxTextPerfMetrics *tp = aFontGroup->GetTextPerfMetrics();
     if (tp) {
         tp->current.textrunConst++;
@@ -186,7 +186,7 @@ gfxTextRun::~gfxTextRun()
     // been told to release its reference to the group, so we mustn't do that
     // again here.
     if (!mReleasedFontGroup) {
-#ifndef RELEASE_OR_BETA
+#ifdef DEBUG
         gfxTextPerfMetrics *tp = mFontGroup->GetTextPerfMetrics();
         if (tp) {
             tp->current.textrunDestr++;
@@ -2939,7 +2939,7 @@ void gfxFontGroup::ComputeRanges(nsTArray<gfxTextRange>& aRanges,
             FindFontForChar(ch, prevCh, nextCh, aRunScript, prevFont,
                             &matchType);
 
-#ifndef RELEASE_OR_BETA
+#ifdef DEBUG
         if (MOZ_UNLIKELY(mTextPerf)) {
             if (matchType == gfxTextRange::kPrefsFallback) {
                 mTextPerf->current.fallbackPrefs++;
@@ -2998,7 +2998,7 @@ void gfxFontGroup::ComputeRanges(nsTArray<gfxTextRange>& aRanges,
 
     aRanges[lastRangeIndex].end = aLength;
 
-#ifndef RELEASE_OR_BETA
+#ifdef DEBUG
     LogModule* log = mStyle.systemFont
                    ? gfxPlatform::GetLog(eGfxLog_textrunui)
                    : gfxPlatform::GetLog(eGfxLog_textrun);
diff --git a/ipc/chromium/src/base/pickle.h b/ipc/chromium/src/base/pickle.h
index c81f52795..f8634d811 100644
--- a/ipc/chromium/src/base/pickle.h
+++ b/ipc/chromium/src/base/pickle.h
@@ -23,7 +23,7 @@
 #include "mozilla/ipc/Faulty.h"
 #endif
 
-#if !defined(RELEASE_OR_BETA) || defined(DEBUG)
+#if defined(DEBUG)
 #define MOZ_PICKLE_SENTINEL_CHECKING
 #endif
 
diff --git a/ipc/glue/BackgroundImpl.cpp b/ipc/glue/BackgroundImpl.cpp
index 86b619f8f..4c1332f03 100644
--- a/ipc/glue/BackgroundImpl.cpp
+++ b/ipc/glue/BackgroundImpl.cpp
@@ -46,11 +46,7 @@
 #include "nsXPCOMPrivate.h"
 #include "prthread.h"
 
-#ifdef RELEASE_OR_BETA
 #define THREADSAFETY_ASSERT MOZ_ASSERT
-#else
-#define THREADSAFETY_ASSERT MOZ_RELEASE_ASSERT
-#endif
 
 #define CRASH_IN_CHILD_PROCESS(_msg)                                           \
   do {                                                                         \
@@ -332,7 +328,7 @@ class ChildImpl final : public BackgroundChildImpl
   // create the background thread after application shutdown has started.
   static bool sShutdownHasStarted;
 
-#if defined(DEBUG) || !defined(RELEASE_OR_BETA)
+#if defined(DEBUG)
   nsIThread* mBoundThread;
 #endif
 
@@ -352,11 +348,7 @@ public:
   {
     THREADSAFETY_ASSERT(mBoundThread);
 
-#ifdef RELEASE_OR_BETA
     DebugOnly<bool> current;
-#else
-    bool current;
-#endif
     THREADSAFETY_ASSERT(
       NS_SUCCEEDED(mBoundThread->IsOnCurrentThread(&current)));
     THREADSAFETY_ASSERT(current);
@@ -369,7 +361,7 @@ public:
   }
 
   ChildImpl()
-#if defined(DEBUG) || !defined(RELEASE_OR_BETA)
+#if defined(DEBUG)
   : mBoundThread(nullptr)
 #endif
 #ifdef DEBUG
@@ -450,7 +442,7 @@ private:
   {
     THREADSAFETY_ASSERT(!mBoundThread);
 
-#if defined(DEBUG) || !defined(RELEASE_OR_BETA)
+#if defined(DEBUG)
     mBoundThread = NS_GetCurrentThread();
 #endif
 
diff --git a/js/public/Class.h b/js/public/Class.h
index 291695d31..788a97964 100644
--- a/js/public/Class.h
+++ b/js/public/Class.h
@@ -132,16 +132,24 @@ class ObjectOpResult
         Uninitialized = uintptr_t(-1)
     };
 
+    static const uintptr_t SoftFailBit = uintptr_t(1) << (sizeof(uintptr_t) * 8 - 1);
+
     ObjectOpResult() : code_(Uninitialized) {}
 
-    /* Return true if succeed() was called. */
+    /* Return true if succeed() or failSoft() was called. */
     bool ok() const {
         MOZ_ASSERT(code_ != Uninitialized);
-        return code_ == OkCode;
+        return code_ == OkCode || (code_ & SoftFailBit);
     }
 
     explicit operator bool() const { return ok(); }
 
+    /* Return true if succeed() was called. */
+    bool confirmOk() const {
+        MOZ_ASSERT(code_ != Uninitialized);
+        return code_ == OkCode;
+    }
+
     /* Set this ObjectOpResult to true and return true. */
     bool succeed() {
         code_ = OkCode;
@@ -161,10 +169,26 @@ class ObjectOpResult
      */
     bool fail(uint32_t msg) {
         MOZ_ASSERT(msg != OkCode);
+        MOZ_ASSERT((msg & SoftFailBit) == 0);
         code_ = msg;
         return true;
     }
 
+    /*
+     * DEPRECATED: This is a non-standard compatibility hack.
+     *
+     * Set this ObjectOpResult to true, but remembers an error code.
+     * This is used for situations where we really want to fail,
+     * but can't for legacy reasons.
+     *
+     * Always returns true, as a convenience.
+     */
+    bool failSoft(uint32_t msg) {
+        // The msg code is currently never extracted again.
+        code_ = msg | SoftFailBit;
+        return true;
+    }
+
     JS_PUBLIC_API(bool) failCantRedefineProp();
     JS_PUBLIC_API(bool) failReadOnly();
     JS_PUBLIC_API(bool) failGetterOnly();
diff --git a/js/src/builtin/Reflect.cpp b/js/src/builtin/Reflect.cpp
index ab7cca174..a902c90d8 100644
--- a/js/src/builtin/Reflect.cpp
+++ b/js/src/builtin/Reflect.cpp
@@ -44,7 +44,7 @@ Reflect_defineProperty(JSContext* cx, unsigned argc, Value* vp)
     ObjectOpResult result;
     if (!DefineProperty(cx, obj, key, desc, result))
         return false;
-    args.rval().setBoolean(bool(result));
+    args.rval().setBoolean(result.confirmOk());
     return true;
 }
 
@@ -69,7 +69,7 @@ Reflect_deleteProperty(JSContext* cx, unsigned argc, Value* vp)
     ObjectOpResult result;
     if (!DeleteProperty(cx, target, key, result))
         return false;
-    args.rval().setBoolean(bool(result));
+    args.rval().setBoolean(result.confirmOk());
     return true;
 }
 
@@ -178,7 +178,7 @@ Reflect_preventExtensions(JSContext* cx, unsigned argc, Value* vp)
     ObjectOpResult result;
     if (!PreventExtensions(cx, target, result))
         return false;
-    args.rval().setBoolean(bool(result));
+    args.rval().setBoolean(result.confirmOk());
     return true;
 }
 
@@ -207,7 +207,7 @@ Reflect_set(JSContext* cx, unsigned argc, Value* vp)
     RootedValue value(cx, args.get(2));
     if (!SetProperty(cx, target, key, value, receiver, result))
         return false;
-    args.rval().setBoolean(bool(result));
+    args.rval().setBoolean(result.confirmOk());
     return true;
 }
 
@@ -240,7 +240,7 @@ Reflect_setPrototypeOf(JSContext* cx, unsigned argc, Value* vp)
     ObjectOpResult result;
     if (!SetPrototype(cx, obj, proto, result))
         return false;
-    args.rval().setBoolean(bool(result));
+    args.rval().setBoolean(result.confirmOk());
     return true;
 }
 
diff --git a/js/src/builtin/TestingFunctions.cpp b/js/src/builtin/TestingFunctions.cpp
index 188f3ce69..822e460a6 100644
--- a/js/src/builtin/TestingFunctions.cpp
+++ b/js/src/builtin/TestingFunctions.cpp
@@ -123,11 +123,7 @@ GetBuildConfiguration(JSContext* cx, unsigned argc, Value* vp)
     if (!JS_SetProperty(cx, info, "debug", value))
         return false;
 
-#ifdef RELEASE_OR_BETA
     value = BooleanValue(true);
-#else
-    value = BooleanValue(false);
-#endif
     if (!JS_SetProperty(cx, info, "release_or_beta", value))
         return false;
 
diff --git a/js/src/shell/js.cpp b/js/src/shell/js.cpp
index 2b1323ebb..2e6ad5b3e 100644
--- a/js/src/shell/js.cpp
+++ b/js/src/shell/js.cpp
@@ -147,13 +147,9 @@ static const size_t gMaxStackSize = 128 * sizeof(size_t) * 1024;
  */
 static const double MAX_TIMEOUT_SECONDS = 1800.0;
 
-// SharedArrayBuffer and Atomics settings track Firefox.  Choose a custom setting
+// SharedArrayBuffer and Atomics settings track browser. Choose a custom setting
 // with --shared-memory={on,off}.
-#ifndef RELEASE_OR_BETA
 # define SHARED_MEMORY_DEFAULT 1
-#else
-# define SHARED_MEMORY_DEFAULT 0
-#endif
 
 using JobQueue = GCVector<JSObject*, 0, SystemAllocPolicy>;
 
diff --git a/media/ffvpx/ffvpxcommon.mozbuild b/media/ffvpx/ffvpxcommon.mozbuild
index 620158694..b776e45b7 100644
--- a/media/ffvpx/ffvpxcommon.mozbuild
+++ b/media/ffvpx/ffvpxcommon.mozbuild
@@ -98,9 +98,6 @@ DEFINES['HAVE_AV_CONFIG_H'] = True
 if CONFIG['MOZ_DEBUG']:
     # Enable all assertions in debug builds.
     DEFINES['ASSERT_LEVEL'] = 2
-elif not CONFIG['RELEASE_OR_BETA']:
-    # Enable fast assertions in opt builds of Nightly and Aurora.
-    DEFINES['ASSERT_LEVEL'] = 1
 
 # clang-cl's <intrin.h> doesn't work the same as MSVC's.  For details, see:
 #
diff --git a/media/libav/moz.build b/media/libav/moz.build
index ec0de8bd0..9dd0d1bec 100644
--- a/media/libav/moz.build
+++ b/media/libav/moz.build
@@ -69,8 +69,5 @@ ALLOW_COMPILER_WARNINGS = True
 if CONFIG['MOZ_DEBUG']:
     # Enable all assertions in debug builds.
     DEFINES['ASSERT_LEVEL'] = 2
-elif not CONFIG['RELEASE_OR_BETA']:
-    # Enable fast assertions in opt builds of Nightly and Aurora.
-    DEFINES['ASSERT_LEVEL'] = 1
 
 include("libavcommon.mozbuild")
diff --git a/mfbt/Assertions.h b/mfbt/Assertions.h
index 85755ee51..0654cced3 100644
--- a/mfbt/Assertions.h
+++ b/mfbt/Assertions.h
@@ -444,11 +444,7 @@ struct AssertionConditionType
 #  define MOZ_ASSERT(...) do { } while (0)
 #endif /* DEBUG */
 
-#ifdef RELEASE_OR_BETA
-#  define MOZ_DIAGNOSTIC_ASSERT MOZ_ASSERT
-#else
-#  define MOZ_DIAGNOSTIC_ASSERT MOZ_RELEASE_ASSERT
-#endif
+#define MOZ_DIAGNOSTIC_ASSERT MOZ_ASSERT
 
 /*
  * MOZ_ASSERT_IF(cond1, cond2) is equivalent to MOZ_ASSERT(cond2) if cond1 is
diff --git a/netwerk/base/security-prefs.js b/netwerk/base/security-prefs.js
index c615dc555..2d950b992 100644
--- a/netwerk/base/security-prefs.js
+++ b/netwerk/base/security-prefs.js
@@ -94,11 +94,7 @@ pref("security.pki.sha1_enforcement_level", 3);
 // 2: fall back to the subject common name for certificates valid before 23
 //    August 2015 if necessary
 // 3: only use name information from the subject alternative name extension
-#ifdef RELEASE_OR_BETA
 pref("security.pki.name_matching_mode", 1);
-#else
-pref("security.pki.name_matching_mode", 2);
-#endif
 
 // security.pki.netscape_step_up_policy controls how the platform handles the
 // id-Netscape-stepUp OID in extended key usage extensions of CA certificates.
@@ -106,11 +102,7 @@ pref("security.pki.name_matching_mode", 2);
 // 1: it is considered equivalent when the notBefore is before 23 August 2016
 // 2: similarly, but for 23 August 2015
 // 3: it is never considered equivalent
-#ifdef RELEASE_OR_BETA
 pref("security.pki.netscape_step_up_policy", 1);
-#else
-pref("security.pki.netscape_step_up_policy", 2);
-#endif
 
 // Configures Certificate Transparency support mode:
 // 0: Fully disabled.
@@ -152,17 +144,10 @@ pref("security.tls.hello_downgrade_check", true);
 // HSTS Priming
 // If a request is mixed-content, send an HSTS priming request to attempt to
 // see if it is available over HTTPS.
-#ifdef RELEASE_OR_BETA
 // Don't change the order of evaluation of mixed-content and HSTS upgrades in
 // order to be most compatible with current standards
 pref("security.mixed_content.send_hsts_priming", false);
 pref("security.mixed_content.use_hsts", false);
-#else
-// Change the order of evaluation so HSTS upgrades happen before
-// mixed-content blocking
-pref("security.mixed_content.send_hsts_priming", true);
-pref("security.mixed_content.use_hsts", true);
-#endif
 // Approximately 1 week default cache for HSTS priming failures, in seconds
 pref ("security.mixed_content.hsts_priming_cache_timeout", 10080);
 // Force the channel to timeout in 3 seconds if we have not received
diff --git a/netwerk/ipc/NeckoParent.cpp b/netwerk/ipc/NeckoParent.cpp
index ddb6feaa6..063b4b836 100644
--- a/netwerk/ipc/NeckoParent.cpp
+++ b/netwerk/ipc/NeckoParent.cpp
@@ -1,6 +1,4 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set sw=2 ts=8 et tw=80 : */
-
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
@@ -143,11 +141,11 @@ GetRequestingPrincipal(const FTPChannelCreationArgs& aArgs)
 
 // Bug 1289001 - If GetValidatedOriginAttributes returns an error string, that
 // usually leads to a content crash with very little info about the cause.
-// We prefer to crash on the parent, so we get the reason in the crash report.
+// We prefer to crash on the parent.
 static MOZ_COLD
 void CrashWithReason(const char * reason)
 {
-#ifndef RELEASE_OR_BETA
+#ifdef DEBUG
   MOZ_CRASH_UNSAFE_OOL(reason);
 #endif
 }
diff --git a/toolkit/xre/nsAppRunner.cpp b/toolkit/xre/nsAppRunner.cpp
index 3f87a2c83..2f1caf014 100644
--- a/toolkit/xre/nsAppRunner.cpp
+++ b/toolkit/xre/nsAppRunner.cpp
@@ -1003,11 +1003,8 @@ nsXULAppInfo::GetLastRunCrashID(nsAString &aLastRunCrashID)
 NS_IMETHODIMP
 nsXULAppInfo::GetIsReleaseOrBeta(bool* aResult)
 {
-#ifdef RELEASE_OR_BETA
+  // Unused; always returns true.
   *aResult = true;
-#else
-  *aResult = false;
-#endif
   return NS_OK;
 }
 
diff --git a/xpcom/build/IOInterposer.h b/xpcom/build/IOInterposer.h
index 3634572a5..6024e625c 100644
--- a/xpcom/build/IOInterposer.h
+++ b/xpcom/build/IOInterposer.h
@@ -260,14 +260,14 @@ class IOInterposerInit
 public:
   IOInterposerInit()
   {
-#if !defined(RELEASE_OR_BETA)
+#ifdef DEBUG
     IOInterposer::Init();
 #endif
   }
 
   ~IOInterposerInit()
   {
-#if !defined(RELEASE_OR_BETA)
+#ifdef DEBUG
     IOInterposer::Clear();
 #endif
   }
diff --git a/xpcom/system/nsIXULRuntime.idl b/xpcom/system/nsIXULRuntime.idl
index 839fea7ce..b8e9a2fd6 100644
--- a/xpcom/system/nsIXULRuntime.idl
+++ b/xpcom/system/nsIXULRuntime.idl
@@ -150,7 +150,8 @@ interface nsIXULRuntime : nsISupports
   readonly attribute DOMString lastRunCrashID;
 
   /**
-   * True if this is RELEASE_OR_BETA.
+   * True if this is explicitly flagged as release or beta at build time.
+   * Currently unused.
    */
   readonly attribute boolean isReleaseOrBeta;