diff --git a/docshell/test/navigation/file_bug1379762-1.html b/docshell/test/navigation/file_bug1379762-1.html
new file mode 100644
index 0000000000..e8cd8b30b4
--- /dev/null
+++ b/docshell/test/navigation/file_bug1379762-1.html
@@ -0,0 +1,32 @@
+<!DOCTYPE html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8">
+    <title>Bug 1379762</title>
+  </head>
+  <img srcset> <!-- This tries to add load blockers during bfcache restoration -->
+  <script>
+    onunload = null; // enable bfcache
+    opener.is(opener.testCount, 0,
+              "We should only run once; otherwise the loadCount variable makes no sense");
+    var loadCount = 0;
+    onpageshow = function() {
+      ++opener.testCount;
+      if (opener.testCount == 1) {
+        // Navigate forward and then back.
+        setTimeout(function() { location = "goback.html"; }, 0);
+      } else if (opener.testCount == 2) {
+        // Do this async so our load event gets a chance to fire if it plans to
+        // do it.
+        setTimeout(function() {
+          opener.nextTest();
+          window.close();
+        });
+      }
+    };
+    onload = function() {
+      ++loadCount;
+      opener.is(loadCount, 1, "Should only get one onload");
+    }
+  </script>
+</html>
diff --git a/docshell/test/navigation/mochitest.ini b/docshell/test/navigation/mochitest.ini
index 1b5f33c7f5..f3bb3d244f 100644
--- a/docshell/test/navigation/mochitest.ini
+++ b/docshell/test/navigation/mochitest.ini
@@ -59,6 +59,7 @@ skip-if = (toolkit == 'android') || (!debug && (os == 'mac' || os == 'win')) # B
 skip-if = (toolkit == 'android') || (debug && e10s) #too slow on Android 4.3 aws only; bug 1030403; bug 1263213 for debug e10s
 [test_sessionhistory.html]
 skip-if = toolkit == 'android' #RANDOM
+support-files = file_bug1379762-1.html
 [test_sibling-matching-parent.html]
 [test_sibling-off-domain.html]
 [test_triggeringprincipal_frame_nav.html]
diff --git a/docshell/test/navigation/test_sessionhistory.html b/docshell/test/navigation/test_sessionhistory.html
index 452271a41f..b922ce4ea1 100644
--- a/docshell/test/navigation/test_sessionhistory.html
+++ b/docshell/test/navigation/test_sessionhistory.html
@@ -31,7 +31,8 @@ var testFiles =
     "file_nested_frames.html",
     "file_shiftReload_and_pushState.html",
     "file_scrollRestoration.html",
-    "file_bug1300461.html"
+    "file_bug1300461.html",
+    "file_bug1379762-1.html",
   ];
 var testCount = 0; // Used by the test files.
 
diff --git a/layout/base/nsPresContext.cpp b/layout/base/nsPresContext.cpp
index 4a54a84323..3106ff3868 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;
+  // 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));
+    if (HasCachedStyleData()) {
+      MediaFeatureValuesChanged(nsRestyleHint(0), nsChangeHint(0));
+    }
   }
 }
 
