--- a/dom/base/nsContentUtils.cpp
+++ b/dom/base/nsContentUtils.cpp
@@ -1341,42 +1341,16 @@ nsContentUtils::GetParserService()
     if (NS_FAILED(rv)) {
       sParserService = nullptr;
     }
   }
 
   return sParserService;
 }
 
-/**
- * A helper function that parses a sandbox attribute (of an <iframe> or
- * a CSP directive) and converts it to the set of flags used internally.
- *
- * @param sandboxAttr   the sandbox attribute
- * @return              the set of flags (0 if sandboxAttr is null)
- */
-uint32_t
-nsContentUtils::ParseSandboxAttributeToFlags(const nsAttrValue* sandboxAttr)
-{
-  // No sandbox attribute, no sandbox flags.
-  if (!sandboxAttr) { return 0; }
-
-  //  Start off by setting all the restriction flags.
-  uint32_t out = SANDBOX_ALL_FLAGS;
-
-// Macro for updating the flag according to the keywords
-#define SANDBOX_KEYWORD(string, atom, flags)                             \
-  if (sandboxAttr->Contains(nsGkAtoms::atom, eIgnoreCase)) { out &= ~(flags); }
-
-#include "IframeSandboxKeywordList.h"
-
-  return out;
-#undef SANDBOX_KEYWORD
-}
-
 nsIBidiKeyboard*
 nsContentUtils::GetBidiKeyboard()
 {
   if (!sBidiKeyboard) {
     nsresult rv = CallGetService("@mozilla.org/widget/bidikeyboard;1", &sBidiKeyboard);
     if (NS_FAILED(rv)) {
       sBidiKeyboard = nullptr;
     }

--- a/dom/base/nsContentUtils.h
+++ b/dom/base/nsContentUtils.h
@@ -903,25 +903,16 @@ public:
   /**
    * Get the localized string named |aKey| in properties file |aFile|.
    */
   static nsresult GetLocalizedString(PropertiesFile aFile,
                                      const char* aKey,
                                      nsXPIDLString& aResult);
 
   /**
-   * A helper function that parses a sandbox attribute (of an <iframe> or
-   * a CSP directive) and converts it to the set of flags used internally.
-   *
-   * @param sandboxAttr   the sandbox attribute
-   * @return              the set of flags (0 if sandboxAttr is null)
-   */
-  static uint32_t ParseSandboxAttributeToFlags(const nsAttrValue* sandboxAttr);
-
-  /**
    * Helper function that generates a UUID.
    */
   static nsresult GenerateUUIDInPlace(nsID& aUUID);
 
   static bool PrefetchEnabled(nsIDocShell* aDocShell);
 
   /**
    * Fill (with the parameters given) the localized string named |aKey| in

--- a/dom/html/HTMLIFrameElement.cpp
+++ b/dom/html/HTMLIFrameElement.cpp
@@ -242,17 +242,32 @@ HTMLIFrameElement::UnsetAttr(int32_t aNa
 
   return NS_OK;
 }
 
 uint32_t
 HTMLIFrameElement::GetSandboxFlags()
 {
   const nsAttrValue* sandboxAttr = GetParsedAttr(nsGkAtoms::sandbox);
-  return nsContentUtils::ParseSandboxAttributeToFlags(sandboxAttr);
+  // No sandbox attribute, no sandbox flags.
+  if (!sandboxAttr) {
+    return 0;
+  }
+
+  //  Start off by setting all the restriction flags.
+  uint32_t out = SANDBOX_ALL_FLAGS;
+
+// Macro for updating the flag according to the keywords
+#define SANDBOX_KEYWORD(string, atom, flags)                             \
+  if (sandboxAttr->Contains(nsGkAtoms::atom, eIgnoreCase)) { out &= ~(flags); }
+
+#include "IframeSandboxKeywordList.h"
+
+  return out;
+#undef SANDBOX_KEYWORD
 }
 
 JSObject*
 HTMLIFrameElement::WrapNode(JSContext* aCx, JS::Handle<JSObject*> aGivenProto)
 {
   return HTMLIFrameElementBinding::Wrap(aCx, this, aGivenProto);
 }