Revert bug 1284816, bug 1341967, bug 1336153 to postpone bustage on non-x86 archs.

diff --git browser/confvars.sh browser/confvars.sh
index d8dcd99c2757..740d9d3e5fcf 100755
--- browser/confvars.sh
+++ browser/confvars.sh
@@ -30,6 +30,7 @@ if test "$OS_ARCH" = "WINNT"; then
   fi
 fi
 
+MOZ_RUST_MP4PARSE=1
 if test "$NIGHTLY_BUILD"; then
   MOZ_RUST_URLPARSE=1
 fi
diff --git build/moz.configure/rust.configure build/moz.configure/rust.configure
index 267d989f1597..f709820e60ae 100644
--- build/moz.configure/rust.configure
+++ build/moz.configure/rust.configure
@@ -4,10 +4,20 @@
 # 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/.
 
-# Rust is required by `rust_compiler` below. We allow_missing here
-# to propagate failures to the better error message there.
-rustc = check_prog('RUSTC', ['rustc'], allow_missing=True)
-cargo = check_prog('CARGO', ['cargo'], allow_missing=True)
+option('--disable-rust', help='Don\'t include Rust language sources')
+
+@depends('--enable-rust')
+def rust_compiler_names(value):
+    if value:
+        return ['rustc']
+
+@depends('--enable-rust')
+def cargo_binary_names(value):
+    if value:
+        return ['cargo']
+
+rustc = check_prog('RUSTC', rust_compiler_names, allow_missing=True)
+cargo = check_prog('CARGO', cargo_binary_names, allow_missing=True)
 
 @depends_if(rustc)
 @checking('rustc version', lambda info: info.version)
@@ -43,9 +53,12 @@ def cargo_info(cargo):
         version=Version(version),
     )
 
-@depends(rustc_info, cargo_info)
+@depends('--enable-rust', rustc_info, cargo_info)
 @imports(_from='textwrap', _import='dedent')
-def rust_compiler(rustc_info, cargo_info):
+def rust_compiler(value, rustc_info, cargo_info):
+    if not value:
+        return None
+
     if not rustc_info:
         die(dedent('''\
         Rust compiler not found.
@@ -97,6 +110,9 @@ def rust_compiler(rustc_info, cargo_info):
 
     return True
 
+set_define('MOZ_RUST', rust_compiler)
+set_config('MOZ_RUST', rust_compiler)
+
 @template
 def rust_triple_alias(host_or_target):
     """Template defining the alias used for rustc's --target flag.
@@ -227,7 +243,8 @@ set_config('RUST_HOST_TARGET', rust_host_triple)
 
 @depends(rust_target_triple)
 def rust_target_env_name(triple):
-    return triple.upper().replace('-','_')
+    if triple:
+        return triple.upper().replace('-','_')
 
 # We need this to form various Cargo environment variables, as there is no
 # uppercase function in make, and we don't want to shell out just for
@@ -235,5 +252,6 @@ def rust_target_env_name(triple):
 set_config('RUST_TARGET_ENV_NAME', rust_target_env_name)
 
 # Until we remove all the other Rust checks in old-configure.
+add_old_configure_assignment('MOZ_RUST', rust_compiler)
 add_old_configure_assignment('RUSTC', rustc)
 add_old_configure_assignment('RUST_TARGET', rust_target_triple)
diff --git config/rules.mk config/rules.mk
index 94cc5556e3d0..7b143ebc5146 100644
--- config/rules.mk
+++ config/rules.mk
@@ -900,6 +900,7 @@ endif
 
 $(foreach file,$(DUMP_SYMS_TARGETS),$(eval $(call syms_template,$(file),$(file)_syms.track)))
 
+ifdef MOZ_RUST
 cargo_host_flag := --target=$(RUST_HOST_TARGET)
 cargo_target_flag := --target=$(RUST_TARGET)
 
@@ -1055,6 +1056,7 @@ force-cargo-host-program-build:
 
 $(HOST_RUST_PROGRAMS): force-cargo-host-program-build
 endif # HOST_RUST_PROGRAMS
+endif # MOZ_RUST
 
 $(SOBJS):
 	$(REPORT_BUILD)
diff --git dom/media/MediaPrefs.h dom/media/MediaPrefs.h
index 4dcc659222a4..559334d89fd1 100644
--- dom/media/MediaPrefs.h
+++ dom/media/MediaPrefs.h
@@ -183,7 +183,7 @@ private:
   DECL_MEDIA_PREF("media.ogg.flac.enabled",                   FlacInOgg, bool, false);
   DECL_MEDIA_PREF("media.flac.enabled",                       FlacEnabled, bool, true);
 
-#if !defined(RELEASE_OR_BETA)
+#if defined(MOZ_RUST_MP4PARSE) && !defined(RELEASE_OR_BETA)
   DECL_MEDIA_PREF("media.rust.test_mode",                     RustTestMode, bool, false);
 #endif
 
diff --git dom/media/gtest/moz.build dom/media/gtest/moz.build
index c66ac4a9437f..e2203c0a4321 100644
--- dom/media/gtest/moz.build
+++ dom/media/gtest/moz.build
@@ -22,7 +22,6 @@ UNIFIED_SOURCES += [
     'TestMozPromise.cpp',
     'TestMP3Demuxer.cpp',
     'TestMP4Demuxer.cpp',
-    'TestRust.cpp',
     'TestTrackEncoder.cpp',
     'TestVideoSegment.cpp',
     'TestVideoUtils.cpp',
@@ -36,6 +35,9 @@ if CONFIG['MOZ_WEBM_ENCODER']:
         'TestWebMWriter.cpp',
     ]
 
+if CONFIG['MOZ_RUST']:
+    UNIFIED_SOURCES += ['TestRust.cpp',]
+
 TEST_HARNESS_FILES.gtest += [
     '../test/gizmo-frag.mp4',
     '../test/gizmo.mp4',
diff --git media/libcubeb/src/moz.build media/libcubeb/src/moz.build
index c65b53b80f63..8953f646e831 100644
--- media/libcubeb/src/moz.build
+++ media/libcubeb/src/moz.build
@@ -32,7 +32,8 @@ if CONFIG['MOZ_PULSEAUDIO']:
         'cubeb_pulse.c',
     ]
     DEFINES['USE_PULSE'] = True
-    DEFINES['USE_PULSE_RUST'] = True
+    if CONFIG['MOZ_RUST']:
+        DEFINES['USE_PULSE_RUST'] = True
 
 if CONFIG['MOZ_JACK']:
     SOURCES += [
diff --git media/libstagefright/binding/DecoderData.cpp media/libstagefright/binding/DecoderData.cpp
index 109ea329d154..a06e533b1e62 100644
--- media/libstagefright/binding/DecoderData.cpp
+++ media/libstagefright/binding/DecoderData.cpp
@@ -13,9 +13,11 @@
 #include "mozilla/ArrayUtils.h"
 #include "include/ESDS.h"
 
+#ifdef MOZ_RUST_MP4PARSE
 // OpusDecoder header is really needed only by MP4 in rust
 #include "OpusDecoder.h"
 #include "mp4parse.h"
+#endif // MOZ_RUST_MP4PARSE
 
 using namespace stagefright;
 using mozilla::media::TimeUnit;
@@ -177,6 +179,7 @@ MP4VideoInfo::Update(const MetaData* aMetaData, const char* aMimeType)
   FindData(aMetaData, kKeyAVCC, mExtraData);
 }
 
+#ifdef MOZ_RUST_MP4PARSE
 static void
 UpdateTrackProtectedInfo(mozilla::TrackInfo& aConfig,
                          const mp4parse_sinf_info& aSinf)
@@ -263,6 +266,7 @@ MP4VideoInfo::Update(const mp4parse_track_info* track,
     mExtraData->AppendElements(video->extra_data.data, video->extra_data.length);
   }
 }
+#endif // MOZ_RUST_MP4PARSE
 
 bool
 MP4VideoInfo::IsValid() const
diff --git media/libstagefright/binding/MP4Metadata.cpp media/libstagefright/binding/MP4Metadata.cpp
index 5c3810d99a38..5d14dfd8b8a9 100644
--- media/libstagefright/binding/MP4Metadata.cpp
+++ media/libstagefright/binding/MP4Metadata.cpp
@@ -20,14 +20,18 @@
 #include "mp4_demuxer/MP4Metadata.h"
 #include "mp4_demuxer/Stream.h"
 #include "MediaPrefs.h"
+#ifdef MOZ_RUST_MP4PARSE
 #include "mp4parse.h"
+#endif // MOZ_RUST_MP4PARSE
 
 #include <limits>
 #include <stdint.h>
 #include <vector>
 
 
+#ifdef MOZ_RUST_MP4PARSE
 struct FreeMP4Parser { void operator()(mp4parse_parser* aPtr) { mp4parse_free(aPtr); } };
+#endif // MOZ_RUST_MP4PARSE
 
 using namespace stagefright;
 using mozilla::media::TimeUnit;
@@ -105,6 +109,7 @@ private:
   bool mCanSeek;
 };
 
+#ifdef MOZ_RUST_MP4PARSE
 // Wrap an mp4_demuxer::Stream to remember the read offset.
 
 class RustStreamAdaptor {
@@ -151,6 +156,7 @@ private:
   RustStreamAdaptor mRustSource;
   mozilla::UniquePtr<mp4parse_parser, FreeMP4Parser> mRustParser;
 };
+#endif // MOZ_RUST_MP4PARSE
 
 class IndiceWrapperStagefright : public IndiceWrapper {
 public:
@@ -187,6 +193,7 @@ IndiceWrapperStagefright::GetIndice(size_t aIndex, Index::Indice& aIndice) const
   return true;
 }
 
+#ifdef MOZ_RUST_MP4PARSE
 // the owner of mIndice is rust mp4 paser, so lifetime of this class
 // SHOULD NOT longer than rust parser.
 class IndiceWrapperRust : public IndiceWrapper
@@ -232,9 +239,11 @@ IndiceWrapperRust::GetIndice(size_t aIndex, Index::Indice& aIndice) const
   aIndice.sync = indice->sync;
   return true;
 }
+#endif // MOZ_RUST_MP4PARSE
 
 MP4Metadata::MP4Metadata(Stream* aSource)
  : mStagefright(MakeUnique<MP4MetadataStagefright>(aSource))
+#ifdef MOZ_RUST_MP4PARSE
  , mRust(MakeUnique<MP4MetadataRust>(aSource))
  , mPreferRust(MediaPrefs::EnableRustMP4Parser())
  , mReportedAudioTrackTelemetry(false)
@@ -242,6 +251,7 @@ MP4Metadata::MP4Metadata(Stream* aSource)
 #ifndef RELEASE_OR_BETA
  , mRustTestMode(MediaPrefs::RustTestMode())
 #endif
+#endif // MOZ_RUST_MP4PARSE
 {
 }
 
@@ -274,8 +284,11 @@ MP4Metadata::GetNumberTracks(mozilla::TrackInfo::TrackType aType) const
   MP4Metadata::ResultAndTrackCount numTracks =
     mStagefright->GetNumberTracks(aType);
 
+#ifdef MOZ_RUST_MP4PARSE
   if (!mRust) {
+#endif // MOZ_RUST_MP4PARSE
     return numTracks;
+#ifdef MOZ_RUST_MP4PARSE
   }
 
   MP4Metadata::ResultAndTrackCount numTracksRust =
@@ -350,8 +363,10 @@ MP4Metadata::GetNumberTracks(mozilla::TrackInfo::TrackType aType) const
   // Same non-error numbers, just return any.
   // (Choosing Rust here, in case it carries a warning, we'd want to know that.)
   return numTracksRust;
+#endif // MOZ_RUST_MP4PARSE
 }
 
+#ifdef MOZ_RUST_MP4PARSE
 bool MP4Metadata::ShouldPreferRust() const {
   if (!mRust) {
     return false;
@@ -389,6 +404,7 @@ bool MP4Metadata::ShouldPreferRust() const {
   // Otherwise, fall back.
   return false;
 }
+#endif // MOZ_RUST_MP4PARSE
 
 static const char*
 GetDifferentField(const mozilla::TrackInfo& info,
@@ -443,6 +459,7 @@ MP4Metadata::GetTrackInfo(mozilla::TrackInfo::TrackType aType,
   MP4Metadata::ResultAndTrackInfo info =
     mStagefright->GetTrackInfo(aType, aTrackNumber);
 
+#ifdef MOZ_RUST_MP4PARSE
   if (!mRust) {
     return info;
   }
@@ -514,6 +531,7 @@ MP4Metadata::GetTrackInfo(mozilla::TrackInfo::TrackType aType,
   if (mPreferRust) {
     return infoRust;
   }
+#endif // MOZ_RUST_MP4PARSE
 
   return info;
 }
@@ -528,6 +546,7 @@ MP4Metadata::ResultAndCryptoFile
 MP4Metadata::Crypto() const
 {
   MP4Metadata::ResultAndCryptoFile crypto = mStagefright->Crypto();
+#ifdef MOZ_RUST_MP4PARSE
   MP4Metadata::ResultAndCryptoFile rustCrypto = mRust->Crypto();
 
 #ifndef RELEASE_OR_BETA
@@ -548,6 +567,7 @@ MP4Metadata::Crypto() const
   if (mPreferRust) {
     return rustCrypto;
   }
+#endif // MOZ_RUST_MP4PARSE
 
   return crypto;
 }
@@ -556,17 +576,22 @@ MP4Metadata::ResultAndIndice
 MP4Metadata::GetTrackIndice(mozilla::TrackID aTrackID)
 {
   FallibleTArray<Index::Indice> indiceSF;
+#ifdef MOZ_RUST_MP4PARSE
   if (!mPreferRust
 #ifndef RELEASE_OR_BETA
       || mRustTestMode
 #endif
      ) {
+#endif // MOZ_RUST_MP4PARSE
     MediaResult rv = mStagefright->ReadTrackIndex(indiceSF, aTrackID);
     if (NS_FAILED(rv)) {
       return {Move(rv), nullptr};
     }
+#ifdef MOZ_RUST_MP4PARSE
   }
+#endif // MOZ_RUST_MP4PARSE
 
+#ifdef MOZ_RUST_MP4PARSE
   mp4parse_byte_data indiceRust = {};
   if (mPreferRust
 #ifndef RELEASE_OR_BETA
@@ -592,13 +617,18 @@ MP4Metadata::GetTrackIndice(mozilla::TrackID aTrackID)
     }
   }
 #endif
+#endif // MOZ_RUST_MP4PARSE
 
   UniquePtr<IndiceWrapper> indice;
+#ifdef MOZ_RUST_MP4PARSE
   if (mPreferRust) {
     indice = mozilla::MakeUnique<IndiceWrapperRust>(indiceRust);
   } else {
+#endif // MOZ_RUST_MP4PARSE
     indice = mozilla::MakeUnique<IndiceWrapperStagefright>(indiceSF);
+#ifdef MOZ_RUST_MP4PARSE
   }
+#endif // MOZ_RUST_MP4PARSE
 
   return {NS_OK, Move(indice)};
 }
@@ -856,6 +886,7 @@ MP4MetadataStagefright::Metadata(Stream* aSource)
   return {NS_OK, Move(buffer)};
 }
 
+#ifdef MOZ_RUST_MP4PARSE
 bool
 RustStreamAdaptor::Read(uint8_t* buffer, uintptr_t size, size_t* bytes_read)
 {
@@ -1152,5 +1183,6 @@ MP4MetadataRust::Metadata(Stream* aSource)
   MOZ_ASSERT(false, "Not yet implemented");
   return {NS_ERROR_NOT_IMPLEMENTED, nullptr};
 }
+#endif // MOZ_RUST_MP4PARSE
 
 } // namespace mp4_demuxer
diff --git media/libstagefright/binding/include/mp4_demuxer/DecoderData.h media/libstagefright/binding/include/mp4_demuxer/DecoderData.h
index 3cd4b7c142f4..dc25ddf03b10 100644
--- media/libstagefright/binding/include/mp4_demuxer/DecoderData.h
+++ media/libstagefright/binding/include/mp4_demuxer/DecoderData.h
@@ -19,11 +19,13 @@ namespace stagefright
 class MetaData;
 }
 
+#ifdef MOZ_RUST_MP4PARSE
 extern "C" {
 typedef struct mp4parse_track_info mp4parse_track_info;
 typedef struct mp4parse_track_audio_info mp4parse_track_audio_info;
 typedef struct mp4parse_track_video_info mp4parse_track_video_info;
 }
+#endif // MOZ_RUST_MP4PARSE
 
 namespace mp4_demuxer
 {
@@ -71,8 +73,10 @@ public:
   void Update(const stagefright::MetaData* aMetaData,
               const char* aMimeType);
 
+#ifdef MOZ_RUST_MP4PARSE
   void Update(const mp4parse_track_info* track,
               const mp4parse_track_audio_info* audio);
+#endif // MOZ_RUST_MP4PARSE
 
   virtual bool IsValid() const override;
 };
@@ -85,8 +89,10 @@ public:
   void Update(const stagefright::MetaData* aMetaData,
               const char* aMimeType);
 
+#ifdef MOZ_RUST_MP4PARSE
   void Update(const mp4parse_track_info* track,
               const mp4parse_track_video_info* video);
+#endif // MOZ_RUST_MP4PARSE
 
   virtual bool IsValid() const override;
 };
diff --git media/libstagefright/binding/include/mp4_demuxer/MP4Metadata.h media/libstagefright/binding/include/mp4_demuxer/MP4Metadata.h
index 492c9c1c1bc3..e16dbbd1155e 100644
--- media/libstagefright/binding/include/mp4_demuxer/MP4Metadata.h
+++ media/libstagefright/binding/include/mp4_demuxer/MP4Metadata.h
@@ -13,7 +13,9 @@
 #include "MediaInfo.h"
 #include "MediaResult.h"
 #include "Stream.h"
+#ifdef MOZ_RUST_MP4PARSE
 #include "mp4parse.h"
+#endif // MOZ_RUST_MP4PARSE
 
 namespace mp4_demuxer {
 
@@ -82,6 +84,7 @@ public:
 
 private:
   UniquePtr<MP4MetadataStagefright> mStagefright;
+#ifdef MOZ_RUST_MP4PARSE
   UniquePtr<MP4MetadataRust> mRust;
   mutable bool mPreferRust;
   mutable bool mReportedAudioTrackTelemetry;
@@ -90,6 +93,7 @@ private:
   mutable bool mRustTestMode;
 #endif
   bool ShouldPreferRust() const;
+#endif // MOZ_RUST_MP4PARSE
 };
 
 } // namespace mp4_demuxer
diff --git media/libstagefright/gtest/moz.build media/libstagefright/gtest/moz.build
index be4d56fc93f7..66fdd365f8f3 100644
--- media/libstagefright/gtest/moz.build
+++ media/libstagefright/gtest/moz.build
@@ -38,12 +38,13 @@ TEST_HARNESS_FILES.gtest += [
     'test_case_1351094.mp4',
 ]
 
-UNIFIED_SOURCES += ['TestMP4Rust.cpp',]
-TEST_HARNESS_FILES.gtest += [
-    '../../../dom/media/test/street.mp4',
-]
-LOCAL_INCLUDES += [
-    '../binding/include',
-]
+if CONFIG['MOZ_RUST']:
+    UNIFIED_SOURCES += ['TestMP4Rust.cpp',]
+    TEST_HARNESS_FILES.gtest += [
+        '../../../dom/media/test/street.mp4',
+    ]
+    LOCAL_INCLUDES += [
+        '../binding/include',
+    ]
 
 FINAL_LIBRARY = 'xul-gtest'
diff --git media/libstagefright/moz.build media/libstagefright/moz.build
index af5d1194d621..6725a0179989 100644
--- media/libstagefright/moz.build
+++ media/libstagefright/moz.build
@@ -83,9 +83,10 @@ SOURCES += [
     'system/core/libutils/VectorImpl.cpp',
 ]
 
-EXPORTS += [
-    'binding/include/mp4parse.h',
-]
+if CONFIG['MOZ_RUST']:
+    EXPORTS += [
+        'binding/include/mp4parse.h',
+    ]
 
 UNIFIED_SOURCES += [
     'binding/Adts.cpp',
diff --git mobile/android/confvars.sh mobile/android/confvars.sh
index e79b6f5c0707..eb62763acaf7 100644
--- mobile/android/confvars.sh
+++ mobile/android/confvars.sh
@@ -30,6 +30,8 @@ MOZ_XULRUNNER=
 MOZ_CAPTURE=1
 MOZ_RAW=1
 
+MOZ_RUST_MP4PARSE=1
+
 # use custom widget for html:select
 MOZ_USE_NATIVE_POPUP_WINDOWS=1
 
diff --git netwerk/base/moz.build netwerk/base/moz.build
index 61d022a9660e..e5ca1d77d859 100644
--- netwerk/base/moz.build
+++ netwerk/base/moz.build
@@ -256,7 +256,7 @@ UNIFIED_SOURCES += [
     'TLSServerSocket.cpp',
 ]
 
-if CONFIG['MOZ_RUST_URLPARSE']:
+if CONFIG['MOZ_RUST'] and CONFIG['MOZ_RUST_URLPARSE']:
     EXPORTS.mozilla.net += [ 'RustURL.h' ]
     UNIFIED_SOURCES += [ 'RustURL.cpp' ]
 
diff --git netwerk/base/nsStandardURL.cpp netwerk/base/nsStandardURL.cpp
index 608b918a4ecf..20bcdeb34ab8 100644
--- netwerk/base/nsStandardURL.cpp
+++ netwerk/base/nsStandardURL.cpp
@@ -858,6 +858,7 @@ nsStandardURL::BuildNormalizedSpec(const char *spec)
         if (!SegmentIs(spec, mScheme, "resource") &&
             !SegmentIs(spec, mScheme, "chrome")) {
             nsAutoCString ipString;
+#ifdef MOZ_RUST
             if (encHost.Length() > 0 &&
                 encHost.First() == '[' && encHost.Last() == ']' &&
                 ValidIPv6orHostname(encHost.get(), encHost.Length())) {
@@ -866,7 +867,9 @@ nsStandardURL::BuildNormalizedSpec(const char *spec)
                     return rv;
                 }
                 encHost = ipString;
-            } else if (NS_SUCCEEDED(NormalizeIPv4(encHost, ipString))) {
+            } else
+#endif
+            if (NS_SUCCEEDED(NormalizeIPv4(encHost, ipString))) {
                 encHost = ipString;
             }
         }
@@ -2112,6 +2115,7 @@ nsStandardURL::SetHost(const nsACString &input)
 
     if (!SegmentIs(mScheme, "resource") && !SegmentIs(mScheme, "chrome")) {
         nsAutoCString ipString;
+#ifdef MOZ_RUST
         if (hostBuf.Length() > 0 &&
             hostBuf.First() == '[' && hostBuf.Last() == ']' &&
             ValidIPv6orHostname(hostBuf.get(), hostBuf.Length())) {
@@ -2120,7 +2124,9 @@ nsStandardURL::SetHost(const nsACString &input)
                 return rv;
             }
             hostBuf = ipString;
-        } else if (NS_SUCCEEDED(NormalizeIPv4(hostBuf, ipString))) {
+        } else
+#endif
+        if (NS_SUCCEEDED(NormalizeIPv4(hostBuf, ipString))) {
           hostBuf = ipString;
         }
     }
diff --git old-configure.in old-configure.in
index 717a94fcc692..54b29d737cc1 100644
--- old-configure.in
+++ old-configure.in
@@ -2330,9 +2330,14 @@ if test -n "$MOZ_MULET"; then
 fi
 
 # Propagate feature switches for code written in rust from confvars.sh
-if test -n "$MOZ_RUST_URLPARSE"; then
-    AC_DEFINE(MOZ_RUST_URLPARSE)
-    AC_SUBST(MOZ_RUST_URLPARSE)
+if test -n "$MOZ_RUST"; then
+    if test -n "$MOZ_RUST_MP4PARSE"; then
+        AC_DEFINE(MOZ_RUST_MP4PARSE)
+    fi
+    if test -n "$MOZ_RUST_URLPARSE"; then
+        AC_DEFINE(MOZ_RUST_URLPARSE)
+        AC_SUBST(MOZ_RUST_URLPARSE)
+    fi
 fi
 
 AC_SUBST(MOZ_PHOENIX)
diff --git toolkit/components/telemetry/Histograms.json toolkit/components/telemetry/Histograms.json
index 061c55f6a5b6..e49dfd176952 100644
--- toolkit/components/telemetry/Histograms.json
+++ toolkit/components/telemetry/Histograms.json
@@ -8320,7 +8320,8 @@
     "expires_in_version": "60",
     "kind": "boolean",
     "bug_numbers": [1220885],
-    "description": "Whether the rust mp4 demuxer successfully parsed a stream segment."
+    "description": "Whether the rust mp4 demuxer successfully parsed a stream segment.",
+    "cpp_guard": "MOZ_RUST_MP4PARSE"
   },
   "MEDIA_RUST_MP4PARSE_ERROR_CODE": {
     "record_in_processes": ["main", "content"],
@@ -8329,7 +8330,8 @@
     "kind": "enumerated",
     "n_values": 32,
     "bug_numbers": [1238420],
-    "description": "The error code reported when an MP4 parse attempt has failed.0 = OK, 1 = bad argument, 2 = invalid data, 3 = unsupported, 4 = unexpected end of file, 5 = read error."
+    "description": "The error code reported when an MP4 parse attempt has failed.0 = OK, 1 = bad argument, 2 = invalid data, 3 = unsupported, 4 = unexpected end of file, 5 = read error.",
+    "cpp_guard": "MOZ_RUST_MP4PARSE"
   },
   "MEDIA_RUST_MP4PARSE_TRACK_MATCH_AUDIO": {
     "record_in_processes": ["main", "content"],
@@ -8337,7 +8339,8 @@
     "expires_in_version": "60",
     "kind": "boolean",
     "bug_numbers": [1231169],
-    "description": "Whether rust and stagefight mp4 parser audio track results match."
+    "description": "Whether rust and stagefight mp4 parser audio track results match.",
+    "cpp_guard": "MOZ_RUST_MP4PARSE"
   },
   "MEDIA_RUST_MP4PARSE_TRACK_MATCH_VIDEO": {
     "record_in_processes": ["main", "content"],
@@ -8345,7 +8348,8 @@
     "expires_in_version": "60",
     "kind": "boolean",
     "bug_numbers": [1231169],
-    "description": "Whether rust and stagefight mp4 parser video track results match."
+    "description": "Whether rust and stagefight mp4 parser video track results match.",
+    "cpp_guard": "MOZ_RUST_MP4PARSE"
   },
   "MEDIA_WMF_DECODE_ERROR": {
     "record_in_processes": ["main", "content", "gpu"],
diff --git toolkit/library/gtest/moz.build toolkit/library/gtest/moz.build
index 69a8fb1f4893..c684f48e456e 100644
--- toolkit/library/gtest/moz.build
+++ toolkit/library/gtest/moz.build
@@ -7,7 +7,6 @@
 FINAL_TARGET = 'dist/bin/gtest'
 
 USE_LIBS += [
-    'gkrust-gtest',
     'static:xul',
     # xul-gtest is an intermediate static library. It is used as FINAL_TARGET
     # for gtest code.
@@ -21,6 +20,11 @@ USE_LIBS += [
 # before StaticXULComponentStart.
 Libxul('xul-gtest-real')
 
+if CONFIG['MOZ_RUST']:
+    USE_LIBS += [
+        'gkrust-gtest',
+    ]
+
 DIRS += [
     'static',
 ]
diff --git toolkit/library/moz.build toolkit/library/moz.build
index 650f6eaba980..191e90ceb09a 100644
--- toolkit/library/moz.build
+++ toolkit/library/moz.build
@@ -63,7 +63,7 @@ def Libxul(name):
 
     # This option should go away in bug 1290972, but we need to wait until
     # Rust 1.12 has been released.
-    if CONFIG['OS_ARCH'] == 'Darwin':
+    if CONFIG['MOZ_RUST'] and CONFIG['OS_ARCH'] == 'Darwin':
         LDFLAGS += ['-Wl,-no_compact_unwind']
 
 Libxul('xul')
@@ -343,4 +343,5 @@ USE_LIBS += ['StaticXULComponentsEnd']
 # The above library needs to be last for C++ purposes.  This library,
 # however, is entirely composed of Rust code, and needs to come after
 # all the C++ code so any possible C++ -> Rust calls can be resolved.
-USE_LIBS += ['gkrust']
+if CONFIG['MOZ_RUST']:
+    USE_LIBS += ['gkrust']
diff --git toolkit/moz.configure toolkit/moz.configure
index ac9d123224ce..e90da70f0fa5 100644
--- toolkit/moz.configure
+++ toolkit/moz.configure
@@ -88,8 +88,7 @@ include('../js/moz.configure')
 
 # Rust
 # ==============================================================
-include('../build/moz.configure/rust.configure',
-        when='--enable-compile-environment')
+include('../build/moz.configure/rust.configure')
 
 
 # L10N
@@ -623,13 +622,13 @@ id_and_secret_keyfile('Leanplum SDK')
 option('--enable-stylo', nargs='?', choices=('build',),
        help='Include Stylo in the build and/or enable it at runtime')
 
-@depends('--enable-stylo')
-def stylo_config(value):
+@depends('--enable-stylo', '--enable-rust')
+def stylo_config(value, rust_enabled):
     build_stylo = None
     enable_stylo = None
 
     # The default is to not build Stylo at all.
-    if value.origin == 'default':
+    if not rust_enabled or value.origin == 'default':
         pass
     elif value == 'build':
         build_stylo = True
@@ -769,12 +768,14 @@ set_config('SERVO_TARGET_DIR', servo_target_dir)
 option('--enable-webrender', nargs='?', choices=('build',),
        help='Include WebRender in the build and/or enable it at runtime')
 
-@depends('--enable-webrender', milestone)
-def webrender(value, milestone):
+@depends('--enable-webrender', '--enable-rust', milestone)
+def webrender(value, rust_enabled, milestone):
     build_webrender = None
     enable_webrender = None
 
-    if value.origin == 'default':
+    if not rust_enabled:
+        pass
+    elif value.origin == 'default':
         # if nothing is specified, default to just building on Nightly
         build_webrender = milestone.is_nightly
     elif value == 'build':
diff --git toolkit/toolkit.mozbuild toolkit/toolkit.mozbuild
index b845aab48023..9215afc6dd2d 100644
--- toolkit/toolkit.mozbuild
+++ toolkit/toolkit.mozbuild
@@ -133,16 +133,23 @@ if CONFIG['MOZ_PREF_EXTENSIONS']:
 
 DIRS += [
     '/devtools',
-    '/toolkit/library',
-    '/toolkit/library/gtest/rust',
-    '/toolkit/library/rust',
-    '/toolkit/library/StaticXULComponentsEnd',
     '/services',
     '/startupcache',
     '/js/ductwork/debugger',
     '/other-licenses/snappy',
 ]
 
+if CONFIG['MOZ_RUST']:
+    DIRS += [
+        '/toolkit/library/gtest/rust',
+        '/toolkit/library/rust',
+    ]
+
+DIRS += [
+    '/toolkit/library/StaticXULComponentsEnd',
+    '/toolkit/library',
+]
+
 if 'gtk' in CONFIG['MOZ_WIDGET_TOOLKIT']:
     DIRS += ['/toolkit/system/gnome']
 
diff --git toolkit/xre/nsAppRunner.cpp toolkit/xre/nsAppRunner.cpp
index 667c2eb1b365..6fb6cf102baa 100644
--- toolkit/xre/nsAppRunner.cpp
+++ toolkit/xre/nsAppRunner.cpp
@@ -227,11 +227,13 @@
 extern uint32_t gRestartMode;
 extern void InstallSignalHandlers(const char *ProgramName);
 
+#ifdef MOZ_RUST
 // This workaround is fixed in Rust 1.19. For details, see bug 1358151.
 // Implementation in toolkit/library/rust/shared/lib.rs
 extern "C" {
   void rust_init_please_remove_this_after_updating_rust_1_19();
 }
+#endif
 
 #define FILE_COMPATIBILITY_INFO NS_LITERAL_CSTRING("compatibility.ini")
 #define FILE_INVALIDATE_CACHES NS_LITERAL_CSTRING(".purgecaches")
@@ -3122,8 +3124,10 @@ XREMain::XRE_mainInit(bool* aExitFlag)
     return 1;
   *aExitFlag = false;
 
+#ifdef MOZ_RUST
   // This workaround is fixed in Rust 1.19. For details, see bug 1358151.
   rust_init_please_remove_this_after_updating_rust_1_19();
+#endif
 
   atexit(UnexpectedExit);
   auto expectedShutdown = mozilla::MakeScopeExit([&] {
diff --git xpcom/base/nsDebugImpl.cpp xpcom/base/nsDebugImpl.cpp
index e6bb623c258b..c49d61dce605 100644
--- xpcom/base/nsDebugImpl.cpp
+++ xpcom/base/nsDebugImpl.cpp
@@ -148,14 +148,20 @@ nsDebugImpl::Abort(const char* aFile, int32_t aLine)
   return NS_OK;
 }
 
+#ifdef MOZ_RUST
 // From toolkit/library/rust/lib.rs
 extern "C" void intentional_panic(const char* message);
+#endif
 
 NS_IMETHODIMP
 nsDebugImpl::RustPanic(const char* aMessage)
 {
+#ifdef MOZ_RUST
   intentional_panic(aMessage);
   return NS_OK;
+#else
+  return NS_ERROR_NOT_IMPLEMENTED;
+#endif
 }
 
 NS_IMETHODIMP
diff --git xpcom/rust/nsstring/gtest/moz.build xpcom/rust/nsstring/gtest/moz.build
index 197411678815..5bed9e57e57d 100644
--- xpcom/rust/nsstring/gtest/moz.build
+++ xpcom/rust/nsstring/gtest/moz.build
@@ -4,8 +4,9 @@
 # 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/.
 
-UNIFIED_SOURCES += [
-    'Test.cpp'
-]
+if CONFIG['MOZ_RUST']:
+    UNIFIED_SOURCES += [
+        'Test.cpp'
+    ]
 
 FINAL_LIBRARY = 'xul-gtest'