1 files changed, 62 insertions, 0 deletions
diff --git a/layout/base/tests/browser_bug1757410.js b/layout/base/tests/browser_bug1757410.js
new file mode 100644
index 0000000000..59c740e5a8
--- /dev/null
+++ b/layout/base/tests/browser_bug1757410.js
@@ -0,0 +1,62 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const PAGECONTENT =
+  "<!DOCTYPE html>" +
+  "<html>" +
+  "<style>" +
+  "html { " +
+  "  height: 120vh;" +
+  "  overflow-y: scroll;" +
+  "}" +
+  "</style>" +
+  "</html>";
+
+const pageUrl = "data:text/html," + encodeURIComponent(PAGECONTENT);
+
+add_task(async function test() {
+  if (window.devicePixelRatio == 1) {
+    ok(
+      true,
+      "Skip this test since this test is supposed to run on HiDPI mode, " +
+        "the devixePixelRato on this machine is " +
+        window.devicePixelRatio
+    );
+    return;
+  }
+
+  const tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, pageUrl);
+
+  // Scroll the content a bit.
+  const originalScrollPosition = await SpecialPowers.spawn(
+    tab.linkedBrowser,
+    [],
+    async () => {
+      content.document.scrollingElement.scrollTop = 100;
+      return content.document.scrollingElement.scrollTop;
+    }
+  );
+
+  // Disabling HiDPI mode and check the scroll position.
+  SpecialPowers.DOMWindowUtils.setHiDPIMode(false);
+  // Make sure we restore even if this test failed.
+  registerCleanupFunction(() => {
+    SpecialPowers.DOMWindowUtils.restoreHiDPIMode();
+  });
+
+  const scrollPosition = await SpecialPowers.spawn(
+    tab.linkedBrowser,
+    [],
+    async () => {
+      return content.document.scrollingElement.scrollTop;
+    }
+  );
+  is(
+    originalScrollPosition,
+    scrollPosition,
+    "The scroll position should be kept"
+  );
+  BrowserTestUtils.removeTab(tab);
+});