diff --git a/dom/ipc/SharedMap.cpp b/dom/ipc/SharedMap.cpp
index 0b1aec534ad5..deddabdeed55 100644
--- a/dom/ipc/SharedMap.cpp
+++ b/dom/ipc/SharedMap.cpp
@@ -14,6 +14,7 @@
 #include "mozilla/dom/ContentProcessMessageManager.h"
 #include "mozilla/dom/IPCBlobUtils.h"
 #include "mozilla/dom/ScriptSettings.h"
+#include "mozilla/IOBuffers.h"
 #include "mozilla/ScriptPreloader.h"
 
 using namespace mozilla::loader;
diff --git a/js/xpconnect/loader/IOBuffers.h b/js/xpconnect/loader/IOBuffers.h
new file mode 100644
index 000000000000..0f1a863360de
--- /dev/null
+++ b/js/xpconnect/loader/IOBuffers.h
@@ -0,0 +1,148 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2; -*- */
+/* 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/. */
+
+#ifndef IOBuffers_h
+#define IOBuffers_h
+
+#include "mozilla/Assertions.h"
+#include "mozilla/CheckedInt.h"
+#include "mozilla/EndianUtils.h"
+#include "mozilla/EnumSet.h"
+#include "mozilla/Range.h"
+#include "mozilla/Span.h"
+#include "nsString.h"
+#include "nsTArray.h"
+
+namespace mozilla {
+namespace loader {
+
+class OutputBuffer {
+ public:
+  OutputBuffer() {}
+
+  uint8_t* write(size_t size) {
+    auto buf = data.AppendElements(size);
+    cursor_ += size;
+    return buf;
+  }
+
+  void codeUint8(const uint8_t& val) { *write(sizeof val) = val; }
+
+  template <typename T>
+  void codeUint8(const EnumSet<T>& val) {
+    // EnumSets are always represented as uint32_t values, so we need to
+    // assert that the value actually fits in a uint8 before writing it.
+    uint32_t value = val.serialize();
+    codeUint8(CheckedUint8(value).value());
+  }
+
+  void codeUint16(const uint16_t& val) {
+    LittleEndian::writeUint16(write(sizeof val), val);
+  }
+
+  void codeUint32(const uint32_t& val) {
+    LittleEndian::writeUint32(write(sizeof val), val);
+  }
+
+  void codeString(const nsCString& str) {
+    auto len = CheckedUint16(str.Length()).value();
+
+    codeUint16(len);
+    memcpy(write(len), str.BeginReading(), len);
+  }
+
+  size_t cursor() const { return cursor_; }
+
+  uint8_t* Get() { return data.Elements(); }
+
+  const uint8_t* Get() const { return data.Elements(); }
+
+ private:
+  nsTArray<uint8_t> data;
+  size_t cursor_ = 0;
+};
+
+class InputBuffer {
+ public:
+  explicit InputBuffer(const Range<uint8_t>& buffer) : data(buffer) {}
+
+  const uint8_t* read(size_t size) {
+    MOZ_ASSERT(checkCapacity(size));
+
+    auto buf = &data[cursor_];
+    cursor_ += size;
+    return buf;
+  }
+
+  bool codeUint8(uint8_t& val) {
+    if (checkCapacity(sizeof val)) {
+      val = *read(sizeof val);
+    }
+    return !error_;
+  }
+
+  template <typename T>
+  bool codeUint8(EnumSet<T>& val) {
+    uint8_t value;
+    if (codeUint8(value)) {
+      val.deserialize(value);
+    }
+    return !error_;
+  }
+
+  bool codeUint16(uint16_t& val) {
+    if (checkCapacity(sizeof val)) {
+      val = LittleEndian::readUint16(read(sizeof val));
+    }
+    return !error_;
+  }
+
+  bool codeUint32(uint32_t& val) {
+    if (checkCapacity(sizeof val)) {
+      val = LittleEndian::readUint32(read(sizeof val));
+    }
+    return !error_;
+  }
+
+  bool codeString(nsCString& str) {
+    uint16_t len;
+    if (codeUint16(len)) {
+      if (checkCapacity(len)) {
+        str.SetLength(len);
+        memcpy(str.BeginWriting(), read(len), len);
+      }
+    }
+    return !error_;
+  }
+
+  bool error() { return error_; }
+
+  bool finished() { return error_ || !remainingCapacity(); }
+
+  size_t remainingCapacity() { return data.length() - cursor_; }
+
+  size_t cursor() const { return cursor_; }
+
+  const uint8_t* Get() const { return data.begin().get(); }
+
+ private:
+  bool checkCapacity(size_t size) {
+    if (size > remainingCapacity()) {
+      error_ = true;
+    }
+    return !error_;
+  }
+
+  bool error_ = false;
+
+ public:
+  const Range<uint8_t>& data;
+  size_t cursor_ = 0;
+};
+
+} // namespace loader
+} // namespace mozilla
+
+#endif  // IOBuffers_h
diff --git a/js/xpconnect/loader/ScriptPreloader-inl.h b/js/xpconnect/loader/ScriptPreloader-inl.h
index c61366c5a68c..4f37580eb2fe 100644
--- a/js/xpconnect/loader/ScriptPreloader-inl.h
+++ b/js/xpconnect/loader/ScriptPreloader-inl.h
@@ -38,130 +38,6 @@ struct MOZ_RAII AutoSafeJSAPI : public AutoJSAPI {
   AutoSafeJSAPI() { Init(); }
 };
 
-class OutputBuffer {
- public:
-  OutputBuffer() {}
-
-  uint8_t* write(size_t size) {
-    auto buf = data.AppendElements(size);
-    cursor_ += size;
-    return buf;
-  }
-
-  void codeUint8(const uint8_t& val) { *write(sizeof val) = val; }
-
-  template <typename T>
-  void codeUint8(const EnumSet<T>& val) {
-    // EnumSets are always represented as uint32_t values, so we need to
-    // assert that the value actually fits in a uint8 before writing it.
-    uint32_t value = val.serialize();
-    codeUint8(CheckedUint8(value).value());
-  }
-
-  void codeUint16(const uint16_t& val) {
-    LittleEndian::writeUint16(write(sizeof val), val);
-  }
-
-  void codeUint32(const uint32_t& val) {
-    LittleEndian::writeUint32(write(sizeof val), val);
-  }
-
-  void codeString(const nsCString& str) {
-    auto len = CheckedUint16(str.Length()).value();
-
-    codeUint16(len);
-    memcpy(write(len), str.BeginReading(), len);
-  }
-
-  size_t cursor() const { return cursor_; }
-
-  uint8_t* Get() { return data.Elements(); }
-
-  const uint8_t* Get() const { return data.Elements(); }
-
- private:
-  nsTArray<uint8_t> data;
-  size_t cursor_ = 0;
-};
-
-class InputBuffer {
- public:
-  explicit InputBuffer(const Range<uint8_t>& buffer) : data(buffer) {}
-
-  const uint8_t* read(size_t size) {
-    MOZ_ASSERT(checkCapacity(size));
-
-    auto buf = &data[cursor_];
-    cursor_ += size;
-    return buf;
-  }
-
-  bool codeUint8(uint8_t& val) {
-    if (checkCapacity(sizeof val)) {
-      val = *read(sizeof val);
-    }
-    return !error_;
-  }
-
-  template <typename T>
-  bool codeUint8(EnumSet<T>& val) {
-    uint8_t value;
-    if (codeUint8(value)) {
-      val.deserialize(value);
-    }
-    return !error_;
-  }
-
-  bool codeUint16(uint16_t& val) {
-    if (checkCapacity(sizeof val)) {
-      val = LittleEndian::readUint16(read(sizeof val));
-    }
-    return !error_;
-  }
-
-  bool codeUint32(uint32_t& val) {
-    if (checkCapacity(sizeof val)) {
-      val = LittleEndian::readUint32(read(sizeof val));
-    }
-    return !error_;
-  }
-
-  bool codeString(nsCString& str) {
-    uint16_t len;
-    if (codeUint16(len)) {
-      if (checkCapacity(len)) {
-        str.SetLength(len);
-        memcpy(str.BeginWriting(), read(len), len);
-      }
-    }
-    return !error_;
-  }
-
-  bool error() { return error_; }
-
-  bool finished() { return error_ || !remainingCapacity(); }
-
-  size_t remainingCapacity() { return data.length() - cursor_; }
-
-  size_t cursor() const { return cursor_; }
-
-  const uint8_t* Get() const { return data.begin().get(); }
-
- private:
-  bool checkCapacity(size_t size) {
-    if (size > remainingCapacity()) {
-      error_ = true;
-    }
-    return !error_;
-  }
-
-  bool error_ = false;
-
- public:
-  const Range<uint8_t>& data;
-  size_t cursor_ = 0;
-};
-
 template <typename T>
 struct Matcher;
 
diff --git a/js/xpconnect/loader/ScriptPreloader.cpp b/js/xpconnect/loader/ScriptPreloader.cpp
index bfbb87c4b8bb..cbe09f5c6515 100644
--- a/js/xpconnect/loader/ScriptPreloader.cpp
+++ b/js/xpconnect/loader/ScriptPreloader.cpp
@@ -14,6 +14,7 @@
 #include "mozilla/ClearOnShutdown.h"
 #include "mozilla/Components.h"
 #include "mozilla/FileUtils.h"
+#include "mozilla/IOBuffers.h"
 #include "mozilla/Logging.h"
 #include "mozilla/ScopeExit.h"
 #include "mozilla/Services.h"
diff --git a/js/xpconnect/loader/moz.build b/js/xpconnect/loader/moz.build
index 4c7a0165177a..aca9160cce61 100644
--- a/js/xpconnect/loader/moz.build
+++ b/js/xpconnect/loader/moz.build
@@ -31,6 +31,7 @@ EXPORTS += [
 
 EXPORTS.mozilla += [
     'AutoMemMap.h',
+    'IOBuffers.h',
     'ScriptPreloader.h',
     'URLPreloader.h',
 ]