diff --git a/dom/base/nsContentUtils.cpp b/dom/base/nsContentUtils.cpp
index 668e20780e..e484abcf20 100644
--- a/dom/base/nsContentUtils.cpp
+++ b/dom/base/nsContentUtils.cpp
@@ -7058,16 +7058,26 @@ nsContentUtils::HasDistributedChildren(nsIContent* aContent)
 
 // static
 bool
-nsContentUtils::IsForbiddenRequestHeader(const nsACString& aHeader)
+nsContentUtils::IsForbiddenRequestHeader(const nsACString& aHeader,
+                                         const nsACString& aValue)
 {
   if (IsForbiddenSystemRequestHeader(aHeader)) {
     return true;
   }
+  
+  if ((nsContentUtils::IsOverrideMethodHeader(aHeader) &&
+       nsContentUtils::ContainsForbiddenMethod(aValue))) {
+    return true;
+  }
 
-  return StringBeginsWith(aHeader, NS_LITERAL_CSTRING("proxy-"),
-                          nsCaseInsensitiveCStringComparator()) ||
-         StringBeginsWith(aHeader, NS_LITERAL_CSTRING("sec-"),
-                          nsCaseInsensitiveCStringComparator());
+  if (StringBeginsWith(aHeader, NS_LITERAL_CSTRING("proxy-"),
+                       nsCaseInsensitiveCStringComparator()) ||
+      StringBeginsWith(aHeader, NS_LITERAL_CSTRING("sec-"),
+                       nsCaseInsensitiveCStringComparator())) {
+    return true;
+  }
+  
+  return false;
 }
 
 // static
@@ -7096,6 +7106,64 @@ nsContentUtils::IsForbiddenResponseHeader(const nsACString& aHeader)
           aHeader.LowerCaseEqualsASCII("set-cookie2"));
 }
 
+// static 
+bool
+nsContentUtils::IsOverrideMethodHeader(const nsACString& headerName) {
+  return headerName.LowerCaseEqualsASCII("x-http-method-override") ||
+         headerName.LowerCaseEqualsASCII("x-http-method") ||
+         headerName.LowerCaseEqualsASCII("x-method-override");
+}
+
+// static
+bool
+nsContentUtils::ContainsForbiddenMethod(const nsACString& headerValue) {
+  bool hasInsecureMethod = false;
+  nsCCharSeparatedTokenizer tokenizer(headerValue, ',');
+
+  while (tokenizer.hasMoreTokens()) {
+    const nsDependentCSubstring& value = tokenizer.nextToken();
+
+    if (value.LowerCaseEqualsASCII("connect") ||
+        value.LowerCaseEqualsASCII("trace") ||
+        value.LowerCaseEqualsASCII("track")) {
+      hasInsecureMethod = true;
+      break;
+    }
+  }
+
+  return hasInsecureMethod;
+}
+
+// static
+bool nsContentUtils::IsCorsUnsafeRequestHeaderValue(
+    const nsACString& aHeaderValue) {
+  const char* cur = aHeaderValue.BeginReading();
+  const char* end = aHeaderValue.EndReading();
+
+  while (cur != end) {
+    // Implementation of
+    // https://fetch.spec.whatwg.org/#cors-unsafe-request-header-byte Is less
+    // than a space but not a horizontal tab
+    if ((*cur < ' ' && *cur != '\t') || *cur == '"' || *cur == '(' ||
+        *cur == ')' || *cur == ':' || *cur == '<' || *cur == '>' ||
+        *cur == '?' || *cur == '@' || *cur == '[' || *cur == '\\' ||
+        *cur == ']' || *cur == '{' || *cur == '}' ||
+        *cur == 0x7F) {  // 0x75 is DEL
+      return true;
+    }
+    cur++;
+  }
+  return false;
+}
+
+// static
+bool nsContentUtils::IsAllowedNonCorsAccept(const nsACString& aHeaderValue) {
+  if (IsCorsUnsafeRequestHeaderValue(aHeaderValue)) {
+    return false;
+  }
+  return true;
+}
+
 // static
 bool
 nsContentUtils::IsAllowedNonCorsContentType(const nsACString& aHeaderValue)
@@ -7103,6 +7171,10 @@ nsContentUtils::IsAllowedNonCorsContentType(const nsACString& aHeaderValue)
   nsAutoCString contentType;
   nsAutoCString unused;
 
+  if (IsCorsUnsafeRequestHeaderValue(aHeaderValue)) {
+    return false;
+  }
+
   nsresult rv = NS_ParseRequestContentType(aHeaderValue, contentType, unused);
   if (NS_FAILED(rv)) {
     return false;
@@ -7113,6 +7185,41 @@ nsContentUtils::IsAllowedNonCorsContentType(const nsACString& aHeaderValue)
          contentType.LowerCaseEqualsLiteral("multipart/form-data");
 }
 
+// static
+bool nsContentUtils::IsAllowedNonCorsLanguage(const nsACString& aHeaderValue) {
+  const char* cur = aHeaderValue.BeginReading();
+  const char* end = aHeaderValue.EndReading();
+
+  while (cur != end) {
+    if ((*cur >= '0' && *cur <= '9') || (*cur >= 'A' && *cur <= 'Z') ||
+        (*cur >= 'a' && *cur <= 'z') || *cur == ' ' || *cur == '*' ||
+        *cur == ',' || *cur == '-' || *cur == '.' || *cur == ';' ||
+        *cur == '=') {
+      cur++;
+      continue;
+    }
+    return false;
+  }
+  return true;
+}
+
+// static
+bool nsContentUtils::IsCORSSafelistedRequestHeader(const nsACString& aName,
+                                                   const nsACString& aValue) {
+  // See https://fetch.spec.whatwg.org/#cors-safelisted-request-header
+  if (aValue.Length() > 128) {
+    return false;
+  }
+  return (aName.LowerCaseEqualsLiteral("accept") &&
+          nsContentUtils::IsAllowedNonCorsAccept(aValue)) ||
+         (aName.LowerCaseEqualsLiteral("accept-language") &&
+          nsContentUtils::IsAllowedNonCorsLanguage(aValue)) ||
+         (aName.LowerCaseEqualsLiteral("content-language") &&
+          nsContentUtils::IsAllowedNonCorsLanguage(aValue)) ||
+         (aName.LowerCaseEqualsLiteral("content-type") &&
+          nsContentUtils::IsAllowedNonCorsContentType(aValue));
+}
+
 bool
 nsContentUtils::DOMWindowDumpEnabled()
 {
diff --git a/dom/base/nsContentUtils.h b/dom/base/nsContentUtils.h
index b3bc22f286..8597e137ef 100644
--- a/dom/base/nsContentUtils.h
+++ b/dom/base/nsContentUtils.h
@@ -2425,7 +2425,8 @@ public:
    * Returns whether a given header is forbidden for an XHR or fetch
    * request.
    */
-  static bool IsForbiddenRequestHeader(const nsACString& aHeader);
+  static bool IsForbiddenRequestHeader(const nsACString& aHeader,
+                                       const nsACString& aValue);
 
   /**
    * Returns whether a given header is forbidden for a system XHR
@@ -2433,18 +2434,50 @@ public:
    */
   static bool IsForbiddenSystemRequestHeader(const nsACString& aHeader);
 
+  /**
+   * Returns whether a given header has characters that aren't permitted
+   */
+  static bool IsCorsUnsafeRequestHeaderValue(const nsACString& aHeaderValue);
+
+  /**
+   * Returns whether a given Accept header value is allowed
+   * for a non-CORS XHR or fetch request.
+   */
+  static bool IsAllowedNonCorsAccept(const nsACString& aHeaderValue);
+
   /**
    * Returns whether a given Content-Type header value is allowed
    * for a non-CORS XHR or fetch request.
    */
   static bool IsAllowedNonCorsContentType(const nsACString& aHeaderValue);
 
+  /**
+   * Returns whether a given Content-Language or accept-language header value is
+   * allowed for a non-CORS XHR or fetch request.
+   */
+  static bool IsAllowedNonCorsLanguage(const nsACString& aHeaderValue);
+ 
+  /**
+   * Returns whether a given header and value is a CORS-safelisted request
+   * header per https://fetch.spec.whatwg.org/#cors-safelisted-request-header
+   */
+  static bool IsCORSSafelistedRequestHeader(const nsACString& aName,
+                                            const nsACString& aValue);
+
   /**
    * Returns whether a given header is forbidden for an XHR or fetch
    * response.
    */
   static bool IsForbiddenResponseHeader(const nsACString& aHeader);
 
+  /**
+   * Checks whether the header overrides any http methods
+   */
+  static bool IsOverrideMethodHeader(const nsACString& headerName);
+  /**
+   * Checks whether the  header value contains any forbidden method
+   */
+  static bool ContainsForbiddenMethod(const nsACString& headerValue);
   /**
    * Returns the inner window ID for the window associated with a request,
    */
diff --git a/dom/fetch/InternalHeaders.cpp b/dom/fetch/InternalHeaders.cpp
index 0448d84731..f4851b7064 100644
--- a/dom/fetch/InternalHeaders.cpp
+++ b/dom/fetch/InternalHeaders.cpp
@@ -5,6 +5,7 @@
 
 #include "mozilla/dom/InternalHeaders.h"
 
+#include "FetchUtil.h"
 #include "mozilla/dom/FetchTypes.h"
 #include "mozilla/ErrorResult.h"
 
@@ -46,20 +47,112 @@ InternalHeaders::ToIPC(nsTArray<HeadersEntry>& aIPCHeaders,
   }
 }
 
+bool
+InternalHeaders::IsValidHeaderValue(const nsCString& aLowerName,
+                                         const nsCString& aNormalizedValue,
+                                         ErrorResult& aRv) {
+  // Steps 2 to 6 for ::Set() and ::Append() in the spec.
+
+  // Step 2
+  if (IsInvalidName(aLowerName, aRv) || IsInvalidValue(aNormalizedValue, aRv)) {
+    return false;
+  }
+
+  // Step 3
+  if (IsImmutable(aRv)) {
+    return false;
+  }
+
+  // Step 4
+  if (mGuard == HeadersGuardEnum::Request) {
+    if (IsForbiddenRequestHeader(aLowerName, aNormalizedValue)) {
+      return false;
+    }
+  }
+
+  // Step 5
+  if (mGuard == HeadersGuardEnum::Request_no_cors) {
+    nsAutoCString tempValue;
+    Get(aLowerName, tempValue, aRv);
+
+    if (tempValue.IsVoid()) {
+      tempValue = aNormalizedValue;
+    } else {
+      tempValue.Append(", ");
+      tempValue.Append(aNormalizedValue);
+    }
+
+    if (!nsContentUtils::IsCORSSafelistedRequestHeader(aLowerName, tempValue)) {
+      return false;
+    }
+  }
+
+  // Step 6
+  else if (IsForbiddenResponseHeader(aLowerName)) {
+    return false;
+  }
+
+  return true;
+}
+
 void
 InternalHeaders::Append(const nsACString& aName, const nsACString& aValue,
                         ErrorResult& aRv)
 {
+  // Step 1
+  nsAutoCString trimValue;
+  NS_TrimHTTPWhitespace(aValue, trimValue);
+   
+  // Steps 2 to 6
   nsAutoCString lowerName;
   ToLowerCase(aName, lowerName);
-
-  if (IsInvalidMutableHeader(lowerName, aValue, aRv)) {
+  if (!IsValidHeaderValue(lowerName, trimValue, aRv)) {
     return;
   }
 
+  // Step 7
   SetListDirty();
-
   mList.AppendElement(Entry(lowerName, aValue));
+
+  // Step 8
+  if (mGuard == HeadersGuardEnum::Request_no_cors) {
+    RemovePrivilegedNoCorsRequestHeaders();
+  }
+}
+
+void InternalHeaders::RemovePrivilegedNoCorsRequestHeaders() {
+  bool dirty = false;
+
+  // remove in reverse order to minimize copying
+  for (int32_t i = mList.Length() - 1; i >= 0; --i) {
+    if (IsPrivilegedNoCorsRequestHeaderName(mList[i].mName)) {
+      mList.RemoveElementAt(i);
+      dirty = true;
+    }
+  }
+
+  if (dirty) {
+    SetListDirty();
+  }
+}
+
+bool InternalHeaders::DeleteInternal(const nsCString& aLowerName,
+                                     ErrorResult& aRv) {
+  bool dirty = false;
+
+  // remove in reverse order to minimize copying
+  for (int32_t i = mList.Length() - 1; i >= 0; --i) {
+    if (mList[i].mName.EqualsIgnoreCase(aLowerName.get())) {
+      mList.RemoveElementAt(i);
+      dirty = true;
+    }
+  }
+
+  if (dirty) {
+    SetListDirty();
+  }
+
+  return dirty;
 }
 
 void
@@ -68,17 +161,43 @@ InternalHeaders::Delete(const nsACString& aName, ErrorResult& aRv)
   nsAutoCString lowerName;
   ToLowerCase(aName, lowerName);
 
-  if (IsInvalidMutableHeader(lowerName, aRv)) {
+  // Step 1
+  if (IsInvalidName(lowerName, aRv)) {
     return;
   }
 
-  SetListDirty();
+  // Step 2
+  if (IsImmutable(aRv)) {
+    return;
+  }
 
-  // remove in reverse order to minimize copying
-  for (int32_t i = mList.Length() - 1; i >= 0; --i) {
-    if (lowerName == mList[i].mName) {
-      mList.RemoveElementAt(i);
-    }
+  // Step 3
+  nsAutoCString value;
+  GetInternal(lowerName, value, aRv);
+  if (IsForbiddenRequestHeader(lowerName, value)) {
+    return;
+  }
+
+  // Step 4
+  if (mGuard == HeadersGuardEnum::Request_no_cors &&
+      !IsNoCorsSafelistedRequestHeaderName(lowerName) &&
+      !IsPrivilegedNoCorsRequestHeaderName(lowerName)) {
+    return;
+  }
+
+  // Step 5
+  if (IsForbiddenResponseHeader(lowerName)) {
+    return;
+  }
+
+  // Steps 6 and 7
+  if (!DeleteInternal(lowerName, aRv)) {
+    return;
+  }
+
+  // Step 8
+  if (mGuard == HeadersGuardEnum::Request_no_cors) {
+    RemovePrivilegedNoCorsRequestHeaders();
   }
 }
 
@@ -91,12 +210,18 @@ InternalHeaders::Get(const nsACString& aName, nsACString& aValue, ErrorResult& a
   if (IsInvalidName(lowerName, aRv)) {
     return;
   }
+  GetInternal(lowerName, aValue, aRv);
+}
 
+void
+InternalHeaders::GetInternal(const nsCString& aLowerName,
+                             nsACString& aValue,
+                             ErrorResult& aRv) const {
   const char* delimiter = ",";
   bool firstValueFound = false;
 
   for (uint32_t i = 0; i < mList.Length(); ++i) {
-    if (lowerName == mList[i].mName) {
+    if (aLowerName == mList[i].mName) {
       if (firstValueFound) {
         aValue += delimiter;
       }
@@ -153,13 +278,18 @@ InternalHeaders::Has(const nsACString& aName, ErrorResult& aRv) const
 void
 InternalHeaders::Set(const nsACString& aName, const nsACString& aValue, ErrorResult& aRv)
 {
+  // Step 1
+  nsAutoCString trimValue;
+  NS_TrimHTTPWhitespace(aValue, trimValue);
+
+  // Steps 2 to 6
   nsAutoCString lowerName;
   ToLowerCase(aName, lowerName);
-
-  if (IsInvalidMutableHeader(lowerName, aValue, aRv)) {
+  if (!IsValidHeaderValue(lowerName, trimValue, aRv)) {
     return;
   }
 
+  // Step 7
   SetListDirty();
 
   int32_t firstIndex = INT32_MAX;
@@ -179,6 +309,11 @@ InternalHeaders::Set(const nsACString& aName, const nsACString& aValue, ErrorRes
   } else {
     mList.AppendElement(Entry(lowerName, aValue));
   }
+
+  // Step 8
+  if (mGuard == HeadersGuardEnum::Request_no_cors) {
+    RemovePrivilegedNoCorsRequestHeaders();
+  }
 }
 
 void
@@ -200,6 +335,22 @@ InternalHeaders::~InternalHeaders()
 {
 }
 
+// static
+bool
+InternalHeaders::IsNoCorsSafelistedRequestHeaderName(const nsCString& aName) {
+  return aName.EqualsIgnoreCase("accept") ||
+         aName.EqualsIgnoreCase("accept-language") ||
+         aName.EqualsIgnoreCase("content-language") ||
+         aName.EqualsIgnoreCase("content-type");
+}
+
+// static
+bool
+InternalHeaders::IsPrivilegedNoCorsRequestHeaderName(
+    const nsCString& aName) {
+  return aName.EqualsIgnoreCase("range");
+}
+
 // static
 bool
 InternalHeaders::IsSimpleHeader(const nsACString& aName, const nsACString& aValue)
@@ -207,9 +358,12 @@ InternalHeaders::IsSimpleHeader(const nsACString& aName, const nsACString& aValu
   // Note, we must allow a null content-type value here to support
   // get("content-type"), but the IsInvalidValue() check will prevent null
   // from being set or appended.
-  return aName.EqualsLiteral("accept") ||
-         aName.EqualsLiteral("accept-language") ||
-         aName.EqualsLiteral("content-language") ||
+  return (aName.EqualsLiteral("accept") &&
+          nsContentUtils::IsAllowedNonCorsAccept(aValue)) ||
+         (aName.EqualsLiteral("accept-language") &&
+          nsContentUtils::IsAllowedNonCorsLanguage(aValue))||
+         (aName.EqualsLiteral("content-language") &&
+          nsContentUtils::IsAllowedNonCorsLanguage(aValue))||
          (aName.EqualsLiteral("content-type") &&
           nsContentUtils::IsAllowedNonCorsContentType(aValue));
 }
@@ -261,10 +415,11 @@ InternalHeaders::IsImmutable(ErrorResult& aRv) const
 }
 
 bool
-InternalHeaders::IsForbiddenRequestHeader(const nsACString& aName) const
+InternalHeaders::IsForbiddenRequestHeader(const nsACString& aName,
+                                          const nsACString& aValue) const
 {
   return mGuard == HeadersGuardEnum::Request &&
-         nsContentUtils::IsForbiddenRequestHeader(aName);
+         nsContentUtils::IsForbiddenRequestHeader(aName, aValue);
 }
 
 bool
@@ -370,7 +525,7 @@ InternalHeaders::CORSHeaders(InternalHeaders* aHeaders, RequestCredentials aCred
   ErrorResult result;
 
   nsAutoCString acExposedNames;
-  aHeaders->GetFirst(NS_LITERAL_CSTRING("Access-Control-Expose-Headers"), acExposedNames, result);
+  aHeaders->Get(NS_LITERAL_CSTRING("Access-Control-Expose-Headers"), acExposedNames, result);
   MOZ_ASSERT(!result.Failed());
 
   bool allowAllHeaders = false;
diff --git a/dom/fetch/InternalHeaders.h b/dom/fetch/InternalHeaders.h
index ae9f2811a2..0a6996ab38 100644
--- a/dom/fetch/InternalHeaders.h
+++ b/dom/fetch/InternalHeaders.h
@@ -136,8 +136,11 @@ private:
 
   static bool IsInvalidName(const nsACString& aName, ErrorResult& aRv);
   static bool IsInvalidValue(const nsACString& aValue, ErrorResult& aRv);
+  bool IsValidHeaderValue(const nsCString& aLowerName,
+                          const nsCString& aNormalizedValue, ErrorResult& aRv);
   bool IsImmutable(ErrorResult& aRv) const;
-  bool IsForbiddenRequestHeader(const nsACString& aName) const;
+  bool IsForbiddenRequestHeader(const nsACString& aName,
+                                const nsACString& aValue) const;
   bool IsForbiddenRequestNoCorsHeader(const nsACString& aName) const;
   bool IsForbiddenRequestNoCorsHeader(const nsACString& aName,
                                       const nsACString& aValue) const;
@@ -156,11 +159,22 @@ private:
     return IsInvalidName(aName, aRv) ||
            IsInvalidValue(aValue, aRv) ||
            IsImmutable(aRv) ||
-           IsForbiddenRequestHeader(aName) ||
+           IsForbiddenRequestHeader(aName, aValue) ||
            IsForbiddenRequestNoCorsHeader(aName, aValue) ||
            IsForbiddenResponseHeader(aName);
   }
 
+  void RemovePrivilegedNoCorsRequestHeaders();
+
+  void GetInternal(const nsCString& aLowerName, nsACString& aValue,
+                   ErrorResult& aRv) const;
+
+  bool DeleteInternal(const nsCString& aLowerName, ErrorResult& aRv);
+
+  static bool IsNoCorsSafelistedRequestHeaderName(const nsCString& aName);
+
+  static bool IsPrivilegedNoCorsRequestHeaderName(const nsCString& aName);
+
   static bool IsSimpleHeader(const nsACString& aName,
                              const nsACString& aValue);
 
diff --git a/dom/xhr/XMLHttpRequestMainThread.cpp b/dom/xhr/XMLHttpRequestMainThread.cpp
index f92ddd35ca..c5b174b5cb 100644
--- a/dom/xhr/XMLHttpRequestMainThread.cpp
+++ b/dom/xhr/XMLHttpRequestMainThread.cpp
@@ -3071,9 +3071,8 @@ XMLHttpRequestMainThread::SetRequestHeader(const nsACString& aName,
   }
 
   // Step 3
-  nsAutoCString value(aValue);
-  static const char kHTTPWhitespace[] = "\n\t\r ";
-  value.Trim(kHTTPWhitespace);
+  nsAutoCString value;
+  NS_TrimHTTPWhitespace(aValue, value);
 
   // Step 4
   if (!NS_IsValidHTTPToken(aName) || !NS_IsReasonableHTTPHeaderValue(value)) {
@@ -3082,7 +3081,7 @@ XMLHttpRequestMainThread::SetRequestHeader(const nsACString& aName,
 
   // Step 5
   bool isPrivilegedCaller = IsSystemXHR();
-  bool isForbiddenHeader = nsContentUtils::IsForbiddenRequestHeader(aName);
+  bool isForbiddenHeader = nsContentUtils::IsForbiddenRequestHeader(aName, aValue);
   if (!isPrivilegedCaller && isForbiddenHeader) {
     NS_ConvertUTF8toUTF16 name(aName);
     const char16_t* params[] = { name.get() };
diff --git a/netwerk/base/nsNetUtil.cpp b/netwerk/base/nsNetUtil.cpp
index ac6f620336..b9ec64ef84 100644
--- a/netwerk/base/nsNetUtil.cpp
+++ b/netwerk/base/nsNetUtil.cpp
@@ -520,6 +520,12 @@ bool NS_IsValidHTTPToken(const nsACString &aToken)
   return mozilla::net::nsHttp::IsValidToken(aToken);
 }
 
+void
+NS_TrimHTTPWhitespace(const nsACString& aSource, nsACString& aDest)
+{
+  mozilla::net::nsHttp::TrimHTTPWhitespace(aSource, aDest);
+}
+
 nsresult
 NS_NewLoadGroup(nsILoadGroup **aResult, nsIPrincipal *aPrincipal)
 {
diff --git a/netwerk/base/nsNetUtil.h b/netwerk/base/nsNetUtil.h
index bd89ca8aeb..385f2c968e 100644
--- a/netwerk/base/nsNetUtil.h
+++ b/netwerk/base/nsNetUtil.h
@@ -959,6 +959,11 @@ bool NS_IsReasonableHTTPHeaderValue(const nsACString &aValue);
  */
 bool NS_IsValidHTTPToken(const nsACString &aToken);
 
+/**
+ * Strip the leading or trailing HTTP whitespace per fetch spec section 2.2.
+ */
+void NS_TrimHTTPWhitespace(const nsACString& aSource, nsACString& aDest);
+
 /**
  * Return true if the given request must be upgraded to HTTPS.
  */
diff --git a/netwerk/protocol/http/nsHttp.cpp b/netwerk/protocol/http/nsHttp.cpp
index faf9e21ffd..88022835e3 100644
--- a/netwerk/protocol/http/nsHttp.cpp
+++ b/netwerk/protocol/http/nsHttp.cpp
@@ -245,6 +245,18 @@ nsHttp::GetProtocolVersion(uint32_t pv)
     }
 }
 
+// static
+void
+nsHttp::TrimHTTPWhitespace(const nsACString& aSource, nsACString& aDest)
+{
+  nsAutoCString str(aSource);
+
+  // HTTP whitespace 0x09: '\t', 0x0A: '\n', 0x0D: '\r', 0x20: ' '
+  static const char kHTTPWhitespace[] = "\t\n\r ";
+  str.Trim(kHTTPWhitespace);
+  aDest.Assign(str);
+}
+
 // static
 bool
 nsHttp::IsReasonableHeaderValue(const nsACString &s)
diff --git a/netwerk/protocol/http/nsHttp.h b/netwerk/protocol/http/nsHttp.h
index a20637808a..b8fee97079 100644
--- a/netwerk/protocol/http/nsHttp.h
+++ b/netwerk/protocol/http/nsHttp.h
@@ -148,6 +148,10 @@ struct nsHttp
     static inline bool IsValidToken(const nsACString &s) {
         return IsValidToken(s.BeginReading(), s.EndReading());
     }
+    
+    // Strip the leading or trailing HTTP whitespace per fetch spec section 2.2.
+    static void TrimHTTPWhitespace(const nsACString& aSource,
+                                   nsACString& aDest);
 
     // Returns true if the specified value is reasonable given the defintion
     // in RFC 2616 section 4.2.  Full strict validation is not performed