1 files changed, 9 insertions, 4 deletions
diff --git a/layout/base/nsPresContext.cpp b/layout/base/nsPresContext.cpp
index 4a54a8432..3106ff386 100644
--- a/layout/base/nsPresContext.cpp
+++ b/layout/base/nsPresContext.cpp
@@ -1307,10 +1307,15 @@ nsPresContext::SetFullZoom(float aZoom)
 void
 nsPresContext::SetOverrideDPPX(float aDPPX)
 {
-  mOverrideDPPX = aDPPX;
-
-  if (HasCachedStyleData()) {
-    MediaFeatureValuesChanged(nsRestyleHint(0), nsChangeHint(0));
+  // SetOverrideDPPX is called during navigations, including history
+  // traversals.  In that case, it's typically called with our current value,
+  // and we don't need to actually do anything.
+  if (aDPPX != mOverrideDPPX) {
+    mOverrideDPPX = aDPPX;
+
+    if (HasCachedStyleData()) {
+      MediaFeatureValuesChanged(nsRestyleHint(0), nsChangeHint(0));
+    }
   }
 }