--- a/layout/base/MobileViewportManager.cpp
+++ b/layout/base/MobileViewportManager.cpp
@@ -83,33 +83,44 @@ MobileViewportManager::Destroy()
   mDocument = nullptr;
   mPresShell = nullptr;
 }
 
 void
 MobileViewportManager::SetRestoreResolution(float aResolution,
                                             LayoutDeviceIntSize aDisplaySize)
 {
-  mRestoreResolution = Some(aResolution);
+  SetRestoreResolution(aResolution);
   ScreenIntSize restoreDisplaySize = ViewAs<ScreenPixel>(aDisplaySize,
     PixelCastJustification::LayoutDeviceIsScreenForBounds);
   mRestoreDisplaySize = Some(restoreDisplaySize);
 }
 
 void
+MobileViewportManager::SetRestoreResolution(float aResolution)
+{
+  mRestoreResolution = Some(aResolution);
+}
+
+void
 MobileViewportManager::RequestReflow()
 {
   MVM_LOG("%p: got a reflow request\n", this);
   RefreshViewportSize(false);
 }
 
 void
 MobileViewportManager::ResolutionUpdated()
 {
   MVM_LOG("%p: resolution updated\n", this);
+  if (!mPainted) {
+    // Save the value, so our default zoom calculation
+    // can take it into account later on.
+    SetRestoreResolution(mPresShell->GetResolution());
+  }
   RefreshSPCSPS();
 }
 
 NS_IMETHODIMP
 MobileViewportManager::HandleEvent(nsIDOMEvent* event)
 {
   nsAutoString type;
   event->GetType(type);

--- a/layout/base/MobileViewportManager.h
+++ b/layout/base/MobileViewportManager.h
@@ -32,16 +32,20 @@ public:
    * resolution computed from the viewport info metadata. This is in the same
    * "units" as the argument to nsDOMWindowUtils::SetResolutionAndScaleTo.
    * Also takes the previous display dimensions as they were at the time the
    * resolution was stored in order to correctly adjust the resolution if the
    * device was rotated in the meantime. */
   void SetRestoreResolution(float aResolution,
                             mozilla::LayoutDeviceIntSize aDisplaySize);
 
+private:
+  void SetRestoreResolution(float aResolution);
+
+public:
   /* Notify the MobileViewportManager that a reflow was requested in the
    * presShell.*/
   void RequestReflow();
 
   /* Notify the MobileViewportManager that the resolution on the presShell was
    * updated, and the SPCSPS needs to be updated. */
   void ResolutionUpdated();
 

--- a/mobile/android/tests/browser/chrome/test_session_scroll_position.html
+++ b/mobile/android/tests/browser/chrome/test_session_scroll_position.html
@@ -206,17 +206,17 @@ https://bugzilla.mozilla.org/show_bug.cg
     pageshow = promiseBrowserEvent(browser, "pageshow");
     scroll = promiseBrowserEvent(browser, "scroll");
     browser.goBack();
     yield pageshow;
     yield scroll;
 
     utils.getResolution(zoom);
     utils.getScrollXY(false, scrollX, scrollY);
-    todo(fuzzyEquals(zoom.value, ZOOM), "zoom restored correctly"); // Bug 1312605
+    ok(fuzzyEquals(zoom.value, ZOOM), "zoom restored correctly");
     is(scrollX.value, SCROLL_X, "scrollX restored correctly");
     is(scrollY.value, SCROLL_Y, "scrollY restored correctly");
 
     // Remove the tab.
     BrowserApp.closeTab(BrowserApp.getTabForBrowser(browser));
   });
 
   add_task(function* test_sessionStoreZoomLevelRecalc() {