--- a/docshell/shistory/nsISHEntry.idl
+++ b/docshell/shistory/nsISHEntry.idl
@@ -134,16 +134,22 @@ interface nsISHEntry : nsISupports
     void setTitle(in AString aTitle);
 
     /** Post Data for the document */
     attribute nsIInputStream postData;
 
     /** LayoutHistoryState for scroll position and form values */
     attribute nsILayoutHistoryState layoutHistoryState;
 
+    /**
+     * Initialises the LayoutHistoryState if it doesn't already exist
+     * and returns a reference to it.
+     */
+    nsILayoutHistoryState initLayoutHistoryState();
+
     /** parent of this entry */
     attribute nsISHEntry parent;
 
     /**
      * The loadType for this entry. This is typically loadHistory except
      * when reload is pressed, it has the appropriate reload flag
      */
     attribute unsigned long loadType;

--- a/docshell/shistory/nsSHEntry.cpp
+++ b/docshell/shistory/nsSHEntry.cpp
@@ -288,16 +288,29 @@ nsSHEntry::SetLayoutHistoryState(nsILayo
     mShared->mLayoutHistoryState->SetScrollPositionOnly(
       !mShared->mSaveLayoutState);
   }
 
   return NS_OK;
 }
 
 NS_IMETHODIMP
+nsSHEntry::InitLayoutHistoryState(nsILayoutHistoryState** aState)
+{
+  if (!mShared->mLayoutHistoryState) {
+    nsCOMPtr<nsILayoutHistoryState> historyState;
+    historyState = NS_NewLayoutHistoryState();
+    nsresult rv = SetLayoutHistoryState(historyState);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  return GetLayoutHistoryState(aState);
+}
+
+NS_IMETHODIMP
 nsSHEntry::GetLoadType(uint32_t* aResult)
 {
   *aResult = mLoadType;
   return NS_OK;
 }
 
 NS_IMETHODIMP
 nsSHEntry::SetLoadType(uint32_t aLoadType)

--- a/layout/base/nsILayoutHistoryState.idl
+++ b/layout/base/nsILayoutHistoryState.idl
@@ -17,19 +17,49 @@ interface nsPresState;
 native constBool(const bool);
 
 %{C++
 #include "nsStringFwd.h"
 
 template<typename> struct already_AddRefed;
 %}
 
-[uuid(aef27cb3-4df9-4eeb-b0b0-ac56cf861d04)]
+[scriptable, uuid(aef27cb3-4df9-4eeb-b0b0-ac56cf861d04)]
 interface nsILayoutHistoryState : nsISupports
 {
+  /**
+  * Whether this LayoutHistoryState contains any PresStates.
+  */
+  readonly attribute boolean hasStates;
+
+  /**
+  * Get the keys of all PresStates held by this LayoutHistoryState.
+  * Note: Check hasStates first.
+  */
+  void getKeys([optional] out uint32_t aCount,
+               [array, size_is(aCount), retval] out string aKeys);
+
+  /*
+  * Attempts to get the data of the PresState corresponding to
+  * the passed key. Throws if no data could be found.
+  */
+  void getPresState(in ACString aKey,
+                    out float aScrollX, out float aScrollY,
+                    out boolean aAllowScrollOriginDowngrade,
+                    out float aRes, out boolean aScaleToRes);
+
+  /**
+   * Constructs a new nsPresState object based on the supplied data
+   * and adds it to the LayoutHistoryState.
+   */
+  void addNewPresState(in ACString aKey,
+                   in float aScrollX, in float aScrollY,
+                   in boolean aAllowScrollOriginDowngrade,
+                   in float aRes, in boolean aScaleToRes);
+
   // Native only interface, converted from the original nsILayoutHistoryState.h
 
   /**
    * Set |aState| as the state object for |aKey|.
    * This _transfers_ownership_ of |aState| to the LayoutHistoryState.
    * It will be freed when RemoveState() is called or when the
    * LayoutHistoryState is destroyed.
    */

--- a/layout/base/nsLayoutHistoryState.cpp
+++ b/layout/base/nsLayoutHistoryState.cpp
@@ -40,16 +40,81 @@ NS_NewLayoutHistoryState()
   RefPtr<nsLayoutHistoryState> state = new nsLayoutHistoryState();
   return state.forget();
 }
 
 NS_IMPL_ISUPPORTS(nsLayoutHistoryState,
                   nsILayoutHistoryState,
                   nsISupportsWeakReference)
 
+NS_IMETHODIMP
+nsLayoutHistoryState::GetHasStates(bool* aHasStates)
+{
+  *aHasStates = HasStates();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLayoutHistoryState::GetKeys(uint32_t* aCount, char*** aKeys)
+{
+  if (!HasStates()) {
+    return NS_ERROR_FAILURE;
+  }
+
+  char** keys =
+    static_cast<char**>(moz_xmalloc(sizeof(char*) * mStates.Count()));
+  *aCount = mStates.Count();
+  *aKeys = keys;
+
+  for (auto iter = mStates.Iter(); !iter.Done(); iter.Next()) {
+    *keys = ToNewCString(iter.Key());
+    keys++;
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLayoutHistoryState::GetPresState(const nsACString& aKey,
+                                   float* aScrollX, float* aScrollY,
+                                   bool* aAllowScrollOriginDowngrade,
+                                   float* aRes, bool* aScaleToRes)
+{
+  nsPresState* state = GetState(nsCString(aKey));
+
+  if (!state) {
+    return NS_ERROR_FAILURE;
+  }
+
+  *aScrollX = state->GetScrollPosition().x;
+  *aScrollY = state->GetScrollPosition().y;
+  *aAllowScrollOriginDowngrade = state->GetAllowScrollOriginDowngrade();
+  *aRes = state->GetResolution();
+  *aScaleToRes = state->GetScaleToResolution();
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLayoutHistoryState::AddNewPresState(const nsACString& aKey,
+                                      float aScrollX, float aScrollY,
+                                      bool aAllowScrollOriginDowngrade,
+                                      float aRes, bool aScaleToRes)
+{
+  nsPresState* newState = new nsPresState();
+  newState->SetScrollState(nsPoint(aScrollX, aScrollY));
+  newState->SetAllowScrollOriginDowngrade(aAllowScrollOriginDowngrade);
+  newState->SetResolution(aRes);
+  newState->SetScaleToResolution(aScaleToRes);
+
+  mStates.Put(nsCString(aKey), newState);
+
+  return NS_OK;
+}
+
 void
 nsLayoutHistoryState::AddState(const nsCString& aStateKey, nsPresState* aState)
 {
   mStates.Put(aStateKey, aState);
 }
 
 nsPresState*
 nsLayoutHistoryState::GetState(const nsCString& aKey)