--- a/docshell/base/nsDocShell.cpp
+++ b/docshell/base/nsDocShell.cpp
@@ -2508,20 +2508,16 @@ nsDocShell::GetFullscreenAllowed(bool* a
   if (mFullscreenAllowed != CHECK_ATTRIBUTES) {
     *aFullscreenAllowed = (mFullscreenAllowed == PARENT_ALLOWS);
     return NS_OK;
   }
 
   // Assume false until we determine otherwise...
   *aFullscreenAllowed = false;
 
-  // If it is sandboxed, fullscreen is not allowed.
-  if (mSandboxFlags & SANDBOXED_FULLSCREEN) {
-    return NS_OK;
-  }
   nsCOMPtr<nsPIDOMWindowOuter> win = GetWindow();
   if (!win) {
     return NS_OK;
   }
   nsCOMPtr<Element> frameElement = win->GetFrameElementInternal();
   if (frameElement && !frameElement->IsXULElement()) {
     // We do not allow document inside any containing element other
     // than iframe to enter fullscreen.

--- a/dom/base/nsSandboxFlags.h
+++ b/dom/base/nsSandboxFlags.h
@@ -80,38 +80,33 @@ const unsigned long SANDBOXED_AUTOMATIC_
 /**
  * This flag prevents URL schemes that use storage areas from being able to
  * access the origin's data.
  */
 // We don't have an explicit representation of this one, apparently?
 // const unsigned long SANDBOXED_STORAGE_AREA_URLS = 0x200;
 
 /**
- * This flag prevents content from using the requestFullscreen() method.
- */
-const unsigned long SANDBOXED_FULLSCREEN = 0x400;
-
-/**
  * This flag blocks the document from changing document.domain.
  */
-const unsigned long SANDBOXED_DOMAIN = 0x800;
+const unsigned long SANDBOXED_DOMAIN = 0x400;
 
 /**
  * This flag prevents content from using window.alert(), window.confirm(),
  * window.print(), window.prompt() and the beforeunload event from putting up
  * dialogs.
  */
-const unsigned long SANDBOXED_MODALS = 0x1000;
+const unsigned long SANDBOXED_MODALS = 0x800;
 
 /**
  * This flag prevents content from escaping the sandbox by ensuring that any
  * auxiliary browsing context it creates inherits the content's active
  * sandboxing flag set.
  */
-const unsigned long SANDBOX_PROPAGATES_TO_AUXILIARY_BROWSING_CONTEXTS = 0x2000;
+const unsigned long SANDBOX_PROPAGATES_TO_AUXILIARY_BROWSING_CONTEXTS = 0x1000;
 
 /**
  * This flag prevents locking screen orientation.
  */
-const unsigned long SANDBOXED_ORIENTATION_LOCK = 0x4000;
+const unsigned long SANDBOXED_ORIENTATION_LOCK = 0x2000;
 
-const unsigned long SANDBOX_ALL_FLAGS = 0x7FFF;
+const unsigned long SANDBOX_ALL_FLAGS = 0x3FFF;
 #endif

--- a/dom/html/HTMLIFrameElement.cpp
+++ b/dom/html/HTMLIFrameElement.cpp
@@ -199,21 +199,17 @@ HTMLIFrameElement::SetAttr(int32_t aName
   return NS_OK;
 }
 
 nsresult
 HTMLIFrameElement::AfterSetAttr(int32_t aNameSpaceID, nsIAtom* aName,
                                 const nsAttrValue* aValue,
                                 bool aNotify)
 {
-  if ((aName == nsGkAtoms::sandbox ||
-       // The allowfullscreen attribute affects the sandboxed fullscreen
-       // flag, thus we should also reapply it if that is changed.
-       aName == nsGkAtoms::allowfullscreen ||
-       aName == nsGkAtoms::mozallowfullscreen) &&
+  if (aName == nsGkAtoms::sandbox &&
       aNameSpaceID == kNameSpaceID_None && mFrameLoader) {
     // If we have an nsFrameLoader, apply the new sandbox flags.
     // Since this is called after the setter, the sandbox flags have
     // alreay been updated.
     mFrameLoader->ApplySandboxFlags(GetSandboxFlags());
   }
   return nsGenericHTMLFrameElement::AfterSetAttr(aNameSpaceID, aName, aValue,
                                                  aNotify);
@@ -239,25 +235,17 @@ HTMLIFrameElement::UnsetAttr(int32_t aNa
 uint32_t
 HTMLIFrameElement::GetSandboxFlags()
 {
   const nsAttrValue* sandboxAttr = GetParsedAttr(nsGkAtoms::sandbox);
   // No sandbox attribute, no sandbox flags.
   if (!sandboxAttr) {
     return SANDBOXED_NONE;
   }
-
-  uint32_t out = nsContentUtils::ParseSandboxAttributeToFlags(sandboxAttr);
-
-  if (GetParsedAttr(nsGkAtoms::allowfullscreen) ||
-      GetParsedAttr(nsGkAtoms::mozallowfullscreen)) {
-    out &= ~SANDBOXED_FULLSCREEN;
-  }
-
-  return out;
+  return nsContentUtils::ParseSandboxAttributeToFlags(sandboxAttr);
 }
 
 JSObject*
 HTMLIFrameElement::WrapNode(JSContext* aCx, JS::Handle<JSObject*> aGivenProto)
 {
   return HTMLIFrameElementBinding::Wrap(aCx, this, aGivenProto);
 }