Bug 1772019 - Wait for PresShell to be initialized before doing WillRefresh tick. r=morgan

Differential Revision: https://phabricator.services.mozilla.com/D147812

accessible/base/NotificationController.cpp

@@ -636,10 +636,10 @@ void NotificationController::WillRefresh(mozilla::TimeStamp aTime) {
   if (!mDocument) return;
 
   // Wait until an update, we have started, or an interruptible reflow is
-  // finished.
+  // finished, and the PresShell has initialized.
   if (mObservingState == eRefreshProcessing ||
       mObservingState == eRefreshProcessingForUpdate ||
-      mPresShell->IsReflowInterrupted()) {
+      mPresShell->IsReflowInterrupted() || !mPresShell->DidInitialize()) {
     return;
   }