--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -5141,22 +5141,24 @@ nsDocument::DispatchContentLoadedEvents(
   mPreloadedPreconnects.Clear();
 
   if (mTiming) {
     mTiming->NotifyDOMContentLoadedStart(nsIDocument::GetDocumentURI());
   }
 
   // Dispatch observer notification to notify observers document is interactive.
   nsCOMPtr<nsIObserverService> os = mozilla::services::GetObserverService();
-  nsIPrincipal *principal = GetPrincipal();
-  os->NotifyObservers(static_cast<nsIDocument*>(this),
-                      nsContentUtils::IsSystemPrincipal(principal) ?
-                        "chrome-document-interactive" :
-                        "content-document-interactive",
-                      nullptr);
+  if (os) {
+    nsIPrincipal *principal = GetPrincipal();
+    os->NotifyObservers(static_cast<nsIDocument*>(this),
+                        nsContentUtils::IsSystemPrincipal(principal) ?
+                          "chrome-document-interactive" :
+                          "content-document-interactive",
+                        nullptr);
+  }
 
   // Fire a DOM event notifying listeners that this document has been
   // loaded (excluding images and other loads initiated by this
   // document).
   nsContentUtils::DispatchTrustedEvent(this, static_cast<nsIDocument*>(this),
                                        NS_LITERAL_STRING("DOMContentLoaded"),
                                        true, false);
 
@@ -9276,25 +9278,27 @@ nsDocument::OnPageShow(bool aPersisted,
 
   nsCOMPtr<EventTarget> target = aDispatchStartTarget;
   if (!target) {
     target = do_QueryInterface(GetWindow());
   }
 
   // Dispatch observer notification to notify observers page is shown.
   nsCOMPtr<nsIObserverService> os = mozilla::services::GetObserverService();
-  nsIPrincipal *principal = GetPrincipal();
-  os->NotifyObservers(static_cast<nsIDocument*>(this),
-                      nsContentUtils::IsSystemPrincipal(principal) ?
-                        "chrome-page-shown" :
-                        "content-page-shown",
-                      nullptr);
-  if (!mObservingAppThemeChanged) {
-    os->AddObserver(this, "app-theme-changed", /* ownsWeak */ false);
-    mObservingAppThemeChanged = true;
+  if (os) {
+    nsIPrincipal *principal = GetPrincipal();
+    os->NotifyObservers(static_cast<nsIDocument*>(this),
+                        nsContentUtils::IsSystemPrincipal(principal) ?
+                          "chrome-page-shown" :
+                          "content-page-shown",
+                        nullptr);
+    if (!mObservingAppThemeChanged) {
+      os->AddObserver(this, "app-theme-changed", /* ownsWeak */ false);
+      mObservingAppThemeChanged = true;
+    }
   }
 
   DispatchPageTransition(target, NS_LITERAL_STRING("pageshow"), aPersisted);
 }
 
 static bool
 NotifyPageHide(nsIDocument* aDocument, void* aData)
 {

--- a/layout/base/nsDocumentViewer.cpp
+++ b/layout/base/nsDocumentViewer.cpp
@@ -972,22 +972,24 @@ nsDocumentViewer::LoadComplete(nsresult 
 
       RefPtr<nsDOMNavigationTiming> timing(d->GetNavigationTiming());
       if (timing) {
         timing->NotifyLoadEventStart();
       }
 
       // Dispatch observer notification to notify observers document load is complete.
       nsCOMPtr<nsIObserverService> os = mozilla::services::GetObserverService();
-      nsIPrincipal *principal = d->NodePrincipal();
-      os->NotifyObservers(d,
-                          nsContentUtils::IsSystemPrincipal(principal) ?
-                          "chrome-document-loaded" :
-                          "content-document-loaded",
-                          nullptr);
+      if (os) {
+        nsIPrincipal *principal = d->NodePrincipal();
+        os->NotifyObservers(d,
+                            nsContentUtils::IsSystemPrincipal(principal) ?
+                            "chrome-document-loaded" :
+                            "content-document-loaded",
+                            nullptr);
+      }
 
       // Notify any devtools about the load.
       RefPtr<TimelineConsumers> timelines = TimelineConsumers::Get();
 
       if (timelines && timelines->HasConsumer(docShell)) {
         timelines->AddMarkerForDocShell(docShell,
           MakeUnique<DocLoadingTimelineMarker>("document::Load"));
       }