--- a/layout/base/PresShell.cpp
+++ b/layout/base/PresShell.cpp
@@ -1858,16 +1858,20 @@ nsresult PresShell::ResizeReflow(nscoord
 }
 
 nsresult PresShell::ResizeReflowIgnoreOverride(nscoord aWidth, nscoord aHeight,
                                                nscoord aOldWidth,
                                                nscoord aOldHeight,
                                                ResizeReflowOptions aOptions) {
   MOZ_ASSERT(!mIsReflowing, "Shouldn't be in reflow here!");
 
+  if (aWidth == aOldWidth && aHeight == aOldHeight) {
+    return NS_OK;
+  }
+
   nsIFrame* rootFrame = mFrameConstructor->GetRootFrame();
   if (!rootFrame) {
     // If we don't have a root frame yet, that means we haven't had our initial
     // reflow... If that's the case, and aWidth or aHeight is unconstrained,
     // ignore them altogether.
     if (aHeight == NS_UNCONSTRAINEDSIZE || aWidth == NS_UNCONSTRAINEDSIZE) {
       // We can't do the work needed for SizeToContent without a root
       // frame, and we want to return before setting the visible area.