diff --git a/dom/fs/api/FileSystemWritableFileStream.cpp b/dom/fs/api/FileSystemWritableFileStream.cpp
index 69d1181c16da..eddd60cade66 100644
--- a/dom/fs/api/FileSystemWritableFileStream.cpp
+++ b/dom/fs/api/FileSystemWritableFileStream.cpp
@@ -382,10 +382,7 @@ already_AddRefed<Promise> FileSystemWritableFileStream::Write(
   RefPtr<Promise> promise = writer->Write(cx, val, aError);
 
   // Step 3. Release writer.
-  {
-    IgnoredErrorResult error;
-    writer->ReleaseLock(cx, error);
-  }
+  writer->ReleaseLock(cx);
 
   // Step 4. Return result.
   return promise.forget();
@@ -423,10 +420,7 @@ already_AddRefed<Promise> FileSystemWritableFileStream::Seek(
   RefPtr<Promise> promise = writer->Write(cx, val, aError);
 
   // Step 3. Release writer.
-  {
-    IgnoredErrorResult error;
-    writer->ReleaseLock(cx, error);
-  }
+  writer->ReleaseLock(cx);
 
   // Step 4. Return result.
   return promise.forget();
@@ -464,10 +458,7 @@ already_AddRefed<Promise> FileSystemWritableFileStream::Truncate(
   RefPtr<Promise> promise = writer->Write(cx, val, aError);
 
   // Step 3. Release writer.
-  {
-    IgnoredErrorResult error;
-    writer->ReleaseLock(cx, error);
-  }
+  writer->ReleaseLock(cx);
 
   // Step 4. Return result.
   return promise.forget();
diff --git a/dom/streams/ReadableStreamBYOBReader.cpp b/dom/streams/ReadableStreamBYOBReader.cpp
index 6c615e03404d..27ca8ce9673b 100644
--- a/dom/streams/ReadableStreamBYOBReader.cpp
+++ b/dom/streams/ReadableStreamBYOBReader.cpp
@@ -60,10 +60,7 @@ void SetUpReadableStreamBYOBReader(ReadableStreamBYOBReader* reader,
   }
 
   // Step 3. Perform ! ReadableStreamReaderGenericInitialize(reader, stream).
-  ReadableStreamReaderGenericInitialize(reader, &stream, rv);
-  if (rv.Failed()) {
-    return;
-  }
+  ReadableStreamReaderGenericInitialize(reader, &stream);
 
   // Step 4. Set reader.[[readIntoRequests]] to a new empty list.
   reader->ReadIntoRequests().clear();
diff --git a/dom/streams/ReadableStreamDefaultReader.cpp b/dom/streams/ReadableStreamDefaultReader.cpp
index 014aca9652b7..c574e4019005 100644
--- a/dom/streams/ReadableStreamDefaultReader.cpp
+++ b/dom/streams/ReadableStreamDefaultReader.cpp
@@ -59,8 +59,7 @@ JSObject* ReadableStreamDefaultReader::WrapObject(
 
 // https://streams.spec.whatwg.org/#readable-stream-reader-generic-initialize
 bool ReadableStreamReaderGenericInitialize(ReadableStreamGenericReader* aReader,
-                                           ReadableStream* aStream,
-                                           ErrorResult& aRv) {
+                                           ReadableStream* aStream) {
   // Step 1.
   aReader->SetStream(aStream);
 
@@ -121,7 +120,7 @@ ReadableStreamDefaultReader::Constructor(const GlobalObject& aGlobal,
 
   // Step 2.
   RefPtr<ReadableStream> streamPtr = &aStream;
-  if (!ReadableStreamReaderGenericInitialize(reader, streamPtr, aRv)) {
+  if (!ReadableStreamReaderGenericInitialize(reader, streamPtr)) {
     return nullptr;
   }
 
@@ -407,7 +406,7 @@ void SetUpReadableStreamDefaultReader(ReadableStreamDefaultReader* aReader,
   }
 
   // Step 2.
-  if (!ReadableStreamReaderGenericInitialize(aReader, aStream, aRv)) {
+  if (!ReadableStreamReaderGenericInitialize(aReader, aStream)) {
     return;
   }
 
diff --git a/dom/streams/ReadableStreamGenericReader.h b/dom/streams/ReadableStreamGenericReader.h
index 8b800fa4ac3b..f85cde59f76e 100644
--- a/dom/streams/ReadableStreamGenericReader.h
+++ b/dom/streams/ReadableStreamGenericReader.h
@@ -63,8 +63,7 @@ class ReadableStreamGenericReader : public nsISupports {
 };
 
 bool ReadableStreamReaderGenericInitialize(ReadableStreamGenericReader* aReader,
-                                           ReadableStream* aStream,
-                                           ErrorResult& aRv);
+                                           ReadableStream* aStream);
 
 void ReadableStreamReaderGenericRelease(ReadableStreamGenericReader* aReader,
                                         ErrorResult& aRv);
diff --git a/dom/streams/ReadableStreamPipeTo.cpp b/dom/streams/ReadableStreamPipeTo.cpp
index 71ddf6d190fe..40e765f9f27f 100644
--- a/dom/streams/ReadableStreamPipeTo.cpp
+++ b/dom/streams/ReadableStreamPipeTo.cpp
@@ -538,9 +538,7 @@ void PipeToPump::Finalize(JSContext* aCx,
                           JS::Handle<mozilla::Maybe<JS::Value>> aError) {
   IgnoredErrorResult rv;
   // Step 1. Perform ! WritableStreamDefaultWriterRelease(writer).
-  WritableStreamDefaultWriterRelease(aCx, mWriter, rv);
-  NS_WARNING_ASSERTION(!rv.Failed(),
-                       "WritableStreamDefaultWriterRelease should not fail.");
+  WritableStreamDefaultWriterRelease(aCx, mWriter);
 
   // Step 2. If reader implements ReadableStreamBYOBReader,
   // perform ! ReadableStreamBYOBReaderRelease(reader).
diff --git a/dom/streams/Transferable.cpp b/dom/streams/Transferable.cpp
index c3aaa93a4be1..41b9256c08fd 100644
--- a/dom/streams/Transferable.cpp
+++ b/dom/streams/Transferable.cpp
@@ -177,7 +177,7 @@ class SetUpTransformWritableMessageEventListener final
   // Note: This promise field is shared with the sink algorithms.
   Promise* BackpressurePromise() { return mBackpressurePromise; }
 
-  void CreateBackpressurePromise(ErrorResult& aRv) {
+  void CreateBackpressurePromise() {
     mBackpressurePromise =
         Promise::CreateInfallible(mController->GetParentObject());
   }
@@ -317,10 +317,7 @@ class CrossRealmWritableUnderlyingSinkAlgorithms final
     // promise resolved with undefined.
     // Note: This promise field is shared with the message event listener.
     if (!mListener->BackpressurePromise()) {
-      mListener->CreateBackpressurePromise(aRv);
-      if (aRv.Failed()) {
-        return nullptr;
-      }
+      mListener->CreateBackpressurePromise();
       mListener->BackpressurePromise()->MaybeResolveWithUndefined();
     }
 
@@ -333,11 +330,7 @@ class CrossRealmWritableUnderlyingSinkAlgorithms final
                MessagePort* aPort,
                JS::Handle<JS::Value> aChunk) -> already_AddRefed<Promise> {
               // Step 2.1: Set backpressurePromise to a new promise.
-              aListener->CreateBackpressurePromise(aRv);
-              if (aRv.Failed()) {
-                aPort->Close();
-                return nullptr;
-              }
+              aListener->CreateBackpressurePromise();
 
               // Step 2.2: Let result be PackAndPostMessageHandlingError(port,
               // "chunk", chunk).
diff --git a/dom/streams/TransformStream.cpp b/dom/streams/TransformStream.cpp
index 6ec994529d2c..b68e2fa89ccd 100644
--- a/dom/streams/TransformStream.cpp
+++ b/dom/streams/TransformStream.cpp
@@ -137,7 +137,7 @@ void TransformStreamErrorWritableAndUnblockWrite(JSContext* aCx,
   // Step 3: If stream.[[backpressure]] is true, perform !
   // TransformStreamSetBackpressure(stream, false).
   if (aStream->Backpressure()) {
-    aStream->SetBackpressure(false, aRv);
+    aStream->SetBackpressure(false);
   }
 }
 
@@ -460,7 +460,7 @@ class TransformStreamUnderlyingSourceAlgorithms final
     MOZ_ASSERT(mStream->BackpressureChangePromise());
 
     // Step 3: Perform ! TransformStreamSetBackpressure(stream, false).
-    mStream->SetBackpressure(false, aRv);
+    mStream->SetBackpressure(false);
 
     // Step 4: Return stream.[[backpressureChangePromise]].
     return do_AddRef(mStream->BackpressureChangePromise());
@@ -506,7 +506,7 @@ NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(
 NS_INTERFACE_MAP_END_INHERITING(UnderlyingSourceAlgorithmsBase)
 
 // https://streams.spec.whatwg.org/#transform-stream-set-backpressure
-void TransformStream::SetBackpressure(bool aBackpressure, ErrorResult& aRv) {
+void TransformStream::SetBackpressure(bool aBackpressure) {
   // Step 1. Assert: stream.[[backpressure]] is not backpressure.
   MOZ_ASSERT(Backpressure() != aBackpressure);
 
@@ -569,7 +569,7 @@ void TransformStream::Initialize(JSContext* aCx, Promise* aStartPromise,
   mBackpressureChangePromise = nullptr;
 
   // Step 10. Perform ! TransformStreamSetBackpressure(stream, true).
-  SetBackpressure(true, aRv);
+  SetBackpressure(true);
   if (aRv.Failed()) {
     return;
   }
diff --git a/dom/streams/TransformStream.h b/dom/streams/TransformStream.h
index 178a04388ab8..453c9de5527e 100644
--- a/dom/streams/TransformStream.h
+++ b/dom/streams/TransformStream.h
@@ -40,7 +40,7 @@ class TransformStream final : public nsISupports, public nsWrapperCache {
   // Internal slot accessors
   bool Backpressure() const { return mBackpressure; }
   Promise* BackpressureChangePromise() { return mBackpressureChangePromise; }
-  void SetBackpressure(bool aBackpressure, ErrorResult& aRv);
+  void SetBackpressure(bool aBackpressure);
   MOZ_KNOWN_LIVE TransformStreamDefaultController* Controller() {
     return mController;
   }
diff --git a/dom/streams/TransformStreamDefaultController.cpp b/dom/streams/TransformStreamDefaultController.cpp
index a75a69bd5885..80a8f702a247 100644
--- a/dom/streams/TransformStreamDefaultController.cpp
+++ b/dom/streams/TransformStreamDefaultController.cpp
@@ -140,7 +140,7 @@ void TransformStreamDefaultController::Enqueue(JSContext* aCx,
     MOZ_ASSERT(backpressure);
 
     // Step 7.2: Perform ! TransformStreamSetBackpressure(true).
-    stream->SetBackpressure(true, aRv);
+    stream->SetBackpressure(true);
   }
 }
 
diff --git a/dom/streams/WritableStream.cpp b/dom/streams/WritableStream.cpp
index 9cd427797374..dec167ef03c4 100644
--- a/dom/streams/WritableStream.cpp
+++ b/dom/streams/WritableStream.cpp
@@ -392,10 +392,7 @@ void WritableStream::StartErroring(JSContext* aCx,
   // Step 8. If writer is not undefined, perform !
   // WritableStreamDefaultWriterEnsureReadyPromiseRejected(writer, reason).
   if (writer) {
-    WritableStreamDefaultWriterEnsureReadyPromiseRejected(writer, aReason, aRv);
-    if (aRv.Failed()) {
-      return;
-    }
+    WritableStreamDefaultWriterEnsureReadyPromiseRejected(writer, aReason);
   }
 
   // Step 9. If ! WritableStreamHasOperationMarkedInFlight(stream) is false
@@ -407,7 +404,7 @@ void WritableStream::StartErroring(JSContext* aCx,
 }
 
 // https://streams.spec.whatwg.org/#writable-stream-update-backpressure
-void WritableStream::UpdateBackpressure(bool aBackpressure, ErrorResult& aRv) {
+void WritableStream::UpdateBackpressure(bool aBackpressure) {
   // Step 1. Assert: stream.[[state]] is "writable".
   MOZ_ASSERT(mState == WriterState::Writable);
   // Step 2. Assert: ! WritableStreamCloseQueuedOrInFlight(stream) is false.
@@ -723,8 +720,8 @@ already_AddRefed<WritableStreamDefaultWriter> WritableStream::GetWriter(
 }
 
 // https://streams.spec.whatwg.org/#writable-stream-add-write-request
-already_AddRefed<Promise> WritableStreamAddWriteRequest(WritableStream* aStream,
-                                                        ErrorResult& aRv) {
+already_AddRefed<Promise> WritableStreamAddWriteRequest(
+    WritableStream* aStream) {
   // Step 1. Assert: ! IsWritableStreamLocked(stream) is true.
   MOZ_ASSERT(IsWritableStreamLocked(aStream));
 
diff --git a/dom/streams/WritableStream.h b/dom/streams/WritableStream.h
index 6797cc04c9f6..4308eb854501 100644
--- a/dom/streams/WritableStream.h
+++ b/dom/streams/WritableStream.h
@@ -142,7 +142,7 @@ class WritableStream : public nsISupports, public nsWrapperCache {
                                         ErrorResult& aRv);
 
   // WritableStreamUpdateBackpressure
-  void UpdateBackpressure(bool aBackpressure, ErrorResult& aRv);
+  void UpdateBackpressure(bool aBackpressure);
 
   // [Transferable]
   // https://html.spec.whatwg.org/multipage/structured-data.html#transfer-steps
@@ -215,8 +215,8 @@ MOZ_CAN_RUN_SCRIPT already_AddRefed<Promise> WritableStreamAbort(
 MOZ_CAN_RUN_SCRIPT already_AddRefed<Promise> WritableStreamClose(
     JSContext* aCx, WritableStream* aStream, ErrorResult& aRv);
 
-already_AddRefed<Promise> WritableStreamAddWriteRequest(WritableStream* aStream,
-                                                        ErrorResult& aRv);
+already_AddRefed<Promise> WritableStreamAddWriteRequest(
+    WritableStream* aStream);
 
 already_AddRefed<WritableStreamDefaultWriter>
 AcquireWritableStreamDefaultWriter(WritableStream* aStream, ErrorResult& aRv);
diff --git a/dom/streams/WritableStreamDefaultController.cpp b/dom/streams/WritableStreamDefaultController.cpp
index 2f0964bc8f24..45cbf553c4be 100644
--- a/dom/streams/WritableStreamDefaultController.cpp
+++ b/dom/streams/WritableStreamDefaultController.cpp
@@ -168,10 +168,7 @@ void SetUpWritableStreamDefaultController(
   bool backpressure = aController->GetBackpressure();
 
   // Step 14. Perform ! WritableStreamUpdateBackpressure(stream, backpressure).
-  aStream->UpdateBackpressure(backpressure, aRv);
-  if (aRv.Failed()) {
-    return;
-  }
+  aStream->UpdateBackpressure(backpressure);
 
   // Step 15. Let startResult be the result of performing startAlgorithm. (This
   // may throw an exception.)
@@ -342,10 +339,7 @@ MOZ_CAN_RUN_SCRIPT static void WritableStreamDefaultControllerProcessWrite(
               bool backpressure = aController->GetBackpressure();
               // Step 4.5.2. Perform ! WritableStreamUpdateBackpressure(stream,
               // backpressure).
-              stream->UpdateBackpressure(backpressure, aRv);
-              if (aRv.Failed()) {
-                return;
-              }
+              stream->UpdateBackpressure(backpressure);
             }
 
             // Step 4.6. Perform !
@@ -483,10 +477,7 @@ void WritableStreamDefaultControllerWrite(
 
     // Step 4.2. Perform ! WritableStreamUpdateBackpressure(stream,
     // backpressure).
-    stream->UpdateBackpressure(backpressure, aRv);
-    if (aRv.Failed()) {
-      return;
-    }
+    stream->UpdateBackpressure(backpressure);
   }
 
   // Step 5. Perform
diff --git a/dom/streams/WritableStreamDefaultWriter.cpp b/dom/streams/WritableStreamDefaultWriter.cpp
index b3728420e890..01bdabafe53f 100644
--- a/dom/streams/WritableStreamDefaultWriter.cpp
+++ b/dom/streams/WritableStreamDefaultWriter.cpp
@@ -206,8 +206,7 @@ already_AddRefed<Promise> WritableStreamDefaultWriter::Close(JSContext* aCx,
 
 // https://streams.spec.whatwg.org/#writable-stream-default-writer-release
 void WritableStreamDefaultWriterRelease(JSContext* aCx,
-                                        WritableStreamDefaultWriter* aWriter,
-                                        ErrorResult& aRv) {
+                                        WritableStreamDefaultWriter* aWriter) {
   // Step 1. Let stream be writer.[[stream]].
   RefPtr<WritableStream> stream = aWriter->GetStream();
 
@@ -229,20 +228,13 @@ void WritableStreamDefaultWriterRelease(JSContext* aCx,
   // Step 5. Perform !
   // WritableStreamDefaultWriterEnsureReadyPromiseRejected(writer,
   // releasedError).
-  WritableStreamDefaultWriterEnsureReadyPromiseRejected(aWriter, releasedError,
-                                                        aRv);
-  if (aRv.Failed()) {
-    return;
-  }
+  WritableStreamDefaultWriterEnsureReadyPromiseRejected(aWriter, releasedError);
 
   // Step 6. Perform !
   // WritableStreamDefaultWriterEnsureClosedPromiseRejected(writer,
   // releasedError).
-  WritableStreamDefaultWriterEnsureClosedPromiseRejected(aWriter, releasedError,
-                                                         aRv);
-  if (aRv.Failed()) {
-    return;
-  }
+  WritableStreamDefaultWriterEnsureClosedPromiseRejected(aWriter,
+                                                         releasedError);
 
   // Step 7. Set stream.[[writer]] to undefined.
   stream->SetWriter(nullptr);
@@ -252,8 +244,7 @@ void WritableStreamDefaultWriterRelease(JSContext* aCx,
 }
 
 // https://streams.spec.whatwg.org/#default-writer-release-lock
-void WritableStreamDefaultWriter::ReleaseLock(JSContext* aCx,
-                                              ErrorResult& aRv) {
+void WritableStreamDefaultWriter::ReleaseLock(JSContext* aCx) {
   // Step 1. Let stream be this.[[stream]].
   RefPtr<WritableStream> stream = mStream;
 
@@ -267,7 +258,7 @@ void WritableStreamDefaultWriter::ReleaseLock(JSContext* aCx,
 
   // Step 4. Perform ! WritableStreamDefaultWriterRelease(this).
   RefPtr<WritableStreamDefaultWriter> thisRefPtr = this;
-  return WritableStreamDefaultWriterRelease(aCx, thisRefPtr, aRv);
+  return WritableStreamDefaultWriterRelease(aCx, thisRefPtr);
 }
 
 // https://streams.spec.whatwg.org/#writable-stream-default-writer-write
@@ -329,10 +320,7 @@ already_AddRefed<Promise> WritableStreamDefaultWriterWrite(
   MOZ_ASSERT(state == WritableStream::WriterState::Writable);
 
   // Step 11. Let promise be ! WritableStreamAddWriteRequest(stream).
-  RefPtr<Promise> promise = WritableStreamAddWriteRequest(stream, aRv);
-  if (aRv.Failed()) {
-    return nullptr;
-  }
+  RefPtr<Promise> promise = WritableStreamAddWriteRequest(stream);
 
   // Step 12. Perform ! WritableStreamDefaultControllerWrite(controller, chunk,
   // chunkSize).
@@ -469,8 +457,7 @@ void SetUpWritableStreamDefaultWriter(WritableStreamDefaultWriter* aWriter,
 
 // https://streams.spec.whatwg.org/#writable-stream-default-writer-ensure-closed-promise-rejected
 void WritableStreamDefaultWriterEnsureClosedPromiseRejected(
-    WritableStreamDefaultWriter* aWriter, JS::Handle<JS::Value> aError,
-    ErrorResult& aRv) {
+    WritableStreamDefaultWriter* aWriter, JS::Handle<JS::Value> aError) {
   RefPtr<Promise> closedPromise = aWriter->ClosedPromise();
   // Step 1. If writer.[[closedPromise]].[[PromiseState]] is "pending", reject
   // writer.[[closedPromise]] with error.
@@ -490,8 +477,7 @@ void WritableStreamDefaultWriterEnsureClosedPromiseRejected(
 
 // https://streams.spec.whatwg.org/#writable-stream-default-writer-ensure-ready-promise-rejected
 void WritableStreamDefaultWriterEnsureReadyPromiseRejected(
-    WritableStreamDefaultWriter* aWriter, JS::Handle<JS::Value> aError,
-    ErrorResult& aRv) {
+    WritableStreamDefaultWriter* aWriter, JS::Handle<JS::Value> aError) {
   RefPtr<Promise> readyPromise = aWriter->ReadyPromise();
   // Step 1. If writer.[[readyPromise]].[[PromiseState]] is "pending", reject
   // writer.[[readyPromise]] with error.
diff --git a/dom/streams/WritableStreamDefaultWriter.h b/dom/streams/WritableStreamDefaultWriter.h
index 0dc60ed6e72c..e9307c6c4586 100644
--- a/dom/streams/WritableStreamDefaultWriter.h
+++ b/dom/streams/WritableStreamDefaultWriter.h
@@ -66,7 +66,7 @@ class WritableStreamDefaultWriter final : public nsISupports,
   MOZ_CAN_RUN_SCRIPT already_AddRefed<Promise> Close(JSContext* aCx,
                                                      ErrorResult& aRv);
 
-  void ReleaseLock(JSContext* aCx, ErrorResult& aRv);
+  void ReleaseLock(JSContext* aCx);
 
   MOZ_CAN_RUN_SCRIPT already_AddRefed<Promise> Write(
       JSContext* aCx, JS::Handle<JS::Value> aChunk, ErrorResult& aRv);
@@ -84,19 +84,16 @@ void SetUpWritableStreamDefaultWriter(WritableStreamDefaultWriter* aWriter,
                                       ErrorResult& aRv);
 
 void WritableStreamDefaultWriterEnsureClosedPromiseRejected(
-    WritableStreamDefaultWriter* aWriter, JS::Handle<JS::Value> aError,
-    ErrorResult& aRv);
+    WritableStreamDefaultWriter* aWriter, JS::Handle<JS::Value> aError);
 
 void WritableStreamDefaultWriterEnsureReadyPromiseRejected(
-    WritableStreamDefaultWriter* aWriter, JS::Handle<JS::Value> aError,
-    ErrorResult& aRv);
+    WritableStreamDefaultWriter* aWriter, JS::Handle<JS::Value> aError);
 
 Nullable<double> WritableStreamDefaultWriterGetDesiredSize(
     WritableStreamDefaultWriter* aWriter);
 
 void WritableStreamDefaultWriterRelease(JSContext* aCx,
-                                        WritableStreamDefaultWriter* aWriter,
-                                        ErrorResult& aRv);
+                                        WritableStreamDefaultWriter* aWriter);
 
 MOZ_CAN_RUN_SCRIPT already_AddRefed<Promise> WritableStreamDefaultWriterWrite(
     JSContext* aCx, WritableStreamDefaultWriter* aWriter,
diff --git a/dom/webidl/WritableStreamDefaultWriter.webidl b/dom/webidl/WritableStreamDefaultWriter.webidl
index 301d8c861f95..e033079f0441 100644
--- a/dom/webidl/WritableStreamDefaultWriter.webidl
+++ b/dom/webidl/WritableStreamDefaultWriter.webidl
@@ -22,7 +22,6 @@ interface WritableStreamDefaultWriter {
   [NewObject]
   Promise<undefined> close();
 
-  [Throws]
   undefined releaseLock();
 
   [NewObject]