From f61ec1c3d77f9f021540641c16b24b80dcb736ab Mon Sep 17 00:00:00 2001
From: Sean Feng <sefeng@mozilla.com>
Date: Thu, 3 Mar 2022 19:13:47 +0000
Subject: [PATCH] Bug 1741671 - Enable BFCache for pages with beforeunload
 event listeners on Desktop r=smaug

The changes only made it works in SHIP(session-history-in-parent) only.

Differential Revision: https://phabricator.services.mozilla.com/D131715
---
 docshell/shistory/nsSHistory.cpp              | 57 ++++++++--------
 .../file_ship_beforeunload_fired.html         | 37 +++++++++++
 docshell/test/navigation/mochitest.ini        | 12 ++++
 .../test_ship_beforeunload_fired.html         | 63 ++++++++++++++++++
 .../test_ship_beforeunload_fired_2.html       | 65 +++++++++++++++++++
 .../test_ship_beforeunload_fired_3.html       | 65 +++++++++++++++++++
 dom/base/Document.cpp                         | 13 ++--
 dom/base/nsGlobalWindowInner.cpp              | 35 +++++++---
 dom/base/nsGlobalWindowInner.h                |  2 +-
 dom/ipc/WindowGlobalParent.cpp                |  1 +
 dom/tests/browser/browser_hasbeforeunload.js  | 18 +++++
 modules/libpref/init/StaticPrefList.yaml      |  7 ++
 .../back-forward-cache/events.html.ini        |  5 +-
 .../tests/browser/dummy_page.html             |  4 +-
 14 files changed, 335 insertions(+), 49 deletions(-)
 create mode 100644 docshell/test/navigation/file_ship_beforeunload_fired.html
 create mode 100644 docshell/test/navigation/test_ship_beforeunload_fired.html
 create mode 100644 docshell/test/navigation/test_ship_beforeunload_fired_2.html
 create mode 100644 docshell/test/navigation/test_ship_beforeunload_fired_3.html

diff --git a/docshell/shistory/nsSHistory.cpp b/docshell/shistory/nsSHistory.cpp
index e74b6230d485..95361d4c5d20 100644
--- a/docshell/shistory/nsSHistory.cpp
+++ b/docshell/shistory/nsSHistory.cpp
@@ -1324,37 +1324,34 @@ void nsSHistory::LoadURIOrBFCache(LoadEntryResult& aLoadEntry) {
                "saving presentation=%i",
                canSave));
 
-      if (!canSave) {
-        nsCOMPtr<nsFrameLoaderOwner> frameLoaderOwner =
-            do_QueryInterface(canonicalBC->GetEmbedderElement());
-        if (frameLoaderOwner) {
-          RefPtr<nsFrameLoader> currentFrameLoader =
-              frameLoaderOwner->GetFrameLoader();
-          if (currentFrameLoader &&
-              currentFrameLoader->GetMaybePendingBrowsingContext()) {
-            WindowGlobalParent* wgp =
-                currentFrameLoader->GetMaybePendingBrowsingContext()
-                    ->Canonical()
-                    ->GetCurrentWindowGlobal();
-            if (wgp) {
-              wgp->PermitUnload([canonicalBC, loadState, she, frameLoader,
-                                 currentFrameLoader](bool aAllow) {
-                if (aAllow) {
-                  FinishRestore(canonicalBC, loadState, she, frameLoader,
-                                false);
-                } else if (currentFrameLoader
-                               ->GetMaybePendingBrowsingContext()) {
-                  nsISHistory* shistory =
-                      currentFrameLoader->GetMaybePendingBrowsingContext()
-                          ->Canonical()
-                          ->GetSessionHistory();
-                  if (shistory) {
-                    shistory->InternalSetRequestedIndex(-1);
-                  }
+      nsCOMPtr<nsFrameLoaderOwner> frameLoaderOwner =
+          do_QueryInterface(canonicalBC->GetEmbedderElement());
+      if (frameLoaderOwner) {
+        RefPtr<nsFrameLoader> currentFrameLoader =
+            frameLoaderOwner->GetFrameLoader();
+        if (currentFrameLoader &&
+            currentFrameLoader->GetMaybePendingBrowsingContext()) {
+          if (WindowGlobalParent* wgp =
+                  currentFrameLoader->GetMaybePendingBrowsingContext()
+                      ->Canonical()
+                      ->GetCurrentWindowGlobal()) {
+            wgp->PermitUnload([canonicalBC, loadState, she, frameLoader,
+                               currentFrameLoader, canSave](bool aAllow) {
+              if (aAllow) {
+                FinishRestore(canonicalBC, loadState, she, frameLoader,
+                              canSave && canonicalBC->AllowedInBFCache(
+                                             Nothing(), nullptr));
+              } else if (currentFrameLoader->GetMaybePendingBrowsingContext()) {
+                nsISHistory* shistory =
+                    currentFrameLoader->GetMaybePendingBrowsingContext()
+                        ->Canonical()
+                        ->GetSessionHistory();
+                if (shistory) {
+                  shistory->InternalSetRequestedIndex(-1);
                 }
-              });
-              return;
-            }
+              }
+            });
+            return;
           }
         }
       }
diff --git a/docshell/test/navigation/file_ship_beforeunload_fired.html b/docshell/test/navigation/file_ship_beforeunload_fired.html
new file mode 100644
index 000000000000..a1f416f959a1
--- /dev/null
+++ b/docshell/test/navigation/file_ship_beforeunload_fired.html
@@ -0,0 +1,37 @@
+<html>
+  <script>
+    onpageshow = function(pageShowEvent) {
+      var bc = new BroadcastChannel("ship_beforeunload");
+      bc.onmessage = function(event) {
+        if (event.data.action == "register_beforeunload") {
+          onbeforeunload = function() {
+            bc.postMessage("beforeunload_fired");
+            bc.close();
+          }
+          if (event.data.loadNextPageFromSessionHistory) {
+            history.back();
+          } else {
+            location.href += "?differentpage";
+          }
+        } else if (event.data.action == "navigate_to_page_b") {
+          bc.close();
+          if (event.data.blockBFCache) {
+            window.blockBFCache = new RTCPeerConnection();
+          }
+          location.href += "?pageb";
+        } else if (event.data.action == "back_to_page_b") {
+          if (event.data.forwardNavigateToPageB) {
+            history.forward();
+          } else {
+            history.back();
+          }
+          bc.close();
+        } else if (event.data.action == "close") {
+          bc.close();
+          window.close();
+        }
+      }
+      bc.postMessage({type: pageShowEvent.type, persisted: pageShowEvent.persisted});
+    }
+  </script>
+</html>
diff --git a/docshell/test/navigation/mochitest.ini b/docshell/test/navigation/mochitest.ini
index e95a1ac0f7db..c18f2d13aac0 100644
--- a/docshell/test/navigation/mochitest.ini
+++ b/docshell/test/navigation/mochitest.ini
@@ -200,3 +200,15 @@ support-files =
 [test_recursive_frames.html]
 [test_bug1699721.html]
 skip-if = !fission # tests fission-only process switching behaviour
+[test_ship_beforeunload_fired.html]
+support-files =
+  file_ship_beforeunload_fired.html
+skip-if = !sessionHistoryInParent
+[test_ship_beforeunload_fired_2.html]
+support-files =
+  file_ship_beforeunload_fired.html
+skip-if = !sessionHistoryInParent
+[test_ship_beforeunload_fired_3.html]
+support-files =
+  file_ship_beforeunload_fired.html
+skip-if = !sessionHistoryInParent
diff --git a/docshell/test/navigation/test_ship_beforeunload_fired.html b/docshell/test/navigation/test_ship_beforeunload_fired.html
new file mode 100644
index 000000000000..e43711676b6f
--- /dev/null
+++ b/docshell/test/navigation/test_ship_beforeunload_fired.html
@@ -0,0 +1,63 @@
+<html>
+  <head>
+    <title>
+      Test that ensures beforeunload is fired when session-history-in-parent is enabled
+    </title>
+    <script src="/tests/SimpleTest/SimpleTest.js"></script>
+    <link rel="stylesheet" href="/tests/SimpleTest/test.css"/>
+  </head>
+  <script>
+    SimpleTest.waitForExplicitFinish();
+
+    /*
+     * This test ensures beforeunload is fired on the current page
+     * when it is entering BFCache and the next page is coming out
+     * from BFCache
+     *
+     * (1) The controller page opens a new window, and page A is loaded there.
+     * (2) Page A then navigates to page B, and a beforeunload event
+     *     listener is registered on page B.
+     * (3) Page B then navigates back to page A, and the beforeunload handler
+     *     should send a message to the controller page.
+     * (4) Page A then navigates back to page B to check if page B has
+     *     been successfully added to BFCache.
+     */
+
+    var bc = new BroadcastChannel("ship_beforeunload");
+    var pageshowCount = 0;
+    var beforeUnloadFired = false;
+    bc.onmessage = function(event) {
+      if (event.data.type == "pageshow") {
+        ++pageshowCount;
+        if (pageshowCount == 1) {
+          bc.postMessage({action: "navigate_to_page_b"});
+        } else if (pageshowCount == 2) {
+          ok(!event.data.persisted, "?pageb shouldn't in BFCache because it's the first navigation");
+          bc.postMessage({action: "register_beforeunload", loadNextPageFromSessionHistory: true});
+        } else if (pageshowCount == 3) {
+          ok(event.data.persisted, "navigated back to page A that was in BFCacache from page B");
+          ok(beforeUnloadFired, "beforeunload has fired on page B");
+          bc.postMessage({action: "back_to_page_b", forwardNavigateToPageB: true});
+        } else if (pageshowCount == 4) {
+          ok(event.data.persisted, "page B has beforeunload fired and also entered BFCache");
+          bc.postMessage({action: "close"});
+          SimpleTest.finish();
+        }
+      } else if (event.data == "beforeunload_fired") {
+        beforeUnloadFired = true;
+      }
+    }
+
+    function runTest() {
+      SpecialPowers.pushPrefEnv({"set": [
+          ["fission.bfcacheInParent", true],
+          ["docshell.shistory.bfcache.ship_allow_beforeunload_listeners", true]
+        ]},
+        function() {
+          window.open("file_ship_beforeunload_fired.html", "", "noopener");
+        }
+      );
+    }
+  </script>
+  <body onload="runTest()"></body>
+</html>
diff --git a/docshell/test/navigation/test_ship_beforeunload_fired_2.html b/docshell/test/navigation/test_ship_beforeunload_fired_2.html
new file mode 100644
index 000000000000..93669502a54e
--- /dev/null
+++ b/docshell/test/navigation/test_ship_beforeunload_fired_2.html
@@ -0,0 +1,65 @@
+<html>
+  <head>
+    <title>
+      Test that ensures beforeunload is fired when session-history-in-parent is enabled
+    </title>
+    <script src="/tests/SimpleTest/SimpleTest.js"></script>
+    <link rel="stylesheet" href="/tests/SimpleTest/test.css"/>
+  </head>
+  <script>
+    SimpleTest.waitForExplicitFinish();
+
+    /*
+     * This test ensures beforeunload is fired on the current page
+     * when it is entering BFCache, and the next page is not coming from
+     * session history and also not coming out from BFCache.
+     *
+     * (1) The controller page opens a new window, and page A is loaded there.
+     * (2) Page A then navigates to page B, and a beforeunload event
+     *     listener is registered on page B.
+     * (3) Page B then navigates to page C, and the beforeunload handler
+     *     should send a message to the controller page.
+     * (4) Page C then navigates back to page B to check if page B has
+     *     been successfully added to BFCache.
+     */
+
+    var bc = new BroadcastChannel("ship_beforeunload");
+    var pageshowCount = 0;
+
+    var beforeUnloadFired = false;
+    bc.onmessage = function(event) {
+      if (event.data.type == "pageshow") {
+        ++pageshowCount;
+        if (pageshowCount == 1) {
+          bc.postMessage({action: "navigate_to_page_b"});
+        } else if (pageshowCount == 2) {
+          ok(!event.data.persisted, "?page B shouldn't in BFCache because it's the first navigation");
+          bc.postMessage({action: "register_beforeunload",
+            loadNextPageFromSessionHistory: false});
+        } else if (pageshowCount == 3) {
+          ok(!event.data.persisted, "navigated to page C that was a new page");
+          ok(beforeUnloadFired, "beforeUnload should be fired on page B");
+          bc.postMessage({action: "back_to_page_b", forwardNavigateToPageB: false});
+        } else if (pageshowCount == 4) {
+          ok(event.data.persisted, "page B has been successfully added to BFCache");
+          bc.postMessage({action: "close"});
+          SimpleTest.finish();
+        }
+      } else if (event.data == "beforeunload_fired") {
+        beforeUnloadFired = true;
+      }
+    }
+
+    function runTest() {
+      SpecialPowers.pushPrefEnv({"set": [
+          ["fission.bfcacheInParent", true],
+          ["docshell.shistory.bfcache.ship_allow_beforeunload_listeners", true]
+        ]},
+        function() {
+          window.open("file_ship_beforeunload_fired.html", "", "noopener");
+        }
+      );
+    }
+  </script>
+  <body onload="runTest()"></body>
+</html>
diff --git a/docshell/test/navigation/test_ship_beforeunload_fired_3.html b/docshell/test/navigation/test_ship_beforeunload_fired_3.html
new file mode 100644
index 000000000000..8951f269c5d6
--- /dev/null
+++ b/docshell/test/navigation/test_ship_beforeunload_fired_3.html
@@ -0,0 +1,65 @@
+<html>
+  <head>
+    <title>
+      Test that ensures beforeunload is fired when session-history-in-parent is enabled
+    </title>
+    <script src="/tests/SimpleTest/SimpleTest.js"></script>
+    <link rel="stylesheet" href="/tests/SimpleTest/test.css"/>
+  </head>
+  <script>
+    SimpleTest.waitForExplicitFinish();
+
+    /*
+     * This test ensures beforeunload is fired on the current page
+     * when it is entering BFCache, and the next page is not coming out
+     * from BFCache, but coming from session history.
+     *
+     * (1) The controller page opens a new window, and page A is loaded there.
+     * (2) Page A then navigates to page B, and a beforeunload event
+     *     listener is registered on page B.
+     * (3) Page B then navigates back to page A, and the beforeunload handler
+     *     should send a message to the controller page.
+     * (4) Page A then navigates back to page B to check if page B has
+     *     been successfully added to BFCache.
+     */
+
+    var bc = new BroadcastChannel("ship_beforeunload");
+    var pageshowCount = 0;
+
+    var beforeUnloadFired = false;
+    bc.onmessage = function(event) {
+      if (event.data.type == "pageshow") {
+        ++pageshowCount;
+        if (pageshowCount == 1) {
+          bc.postMessage({action: "navigate_to_page_b", blockBFCache: true});
+        } else if (pageshowCount == 2) {
+          ok(!event.data.persisted, "?page B shouldn't in BFCache because it's the first navigation");
+          bc.postMessage({action: "register_beforeunload",
+          loadNextPageFromSessionHistory: true});
+        } else if (pageshowCount == 3) {
+          ok(!event.data.persisted, "navigated back to page A that was session history but not in BFCache");
+          ok(beforeUnloadFired, "beforeUnload should be fired on page B");
+          bc.postMessage({action: "back_to_page_b", forwardNavigateToPageB: true});
+        } else if (pageshowCount == 4) {
+          ok(event.data.persisted, "page B has been successfully added to BFCache");
+          bc.postMessage({action: "close"});
+          SimpleTest.finish();
+        }
+      } else if (event.data == "beforeunload_fired") {
+        beforeUnloadFired = true;
+      }
+    }
+
+    function runTest() {
+      SpecialPowers.pushPrefEnv({"set": [
+          ["fission.bfcacheInParent", true],
+          ["docshell.shistory.bfcache.ship_allow_beforeunload_listeners", true]
+        ]},
+        function() {
+          window.open("file_ship_beforeunload_fired.html", "", "noopener");
+        }
+      );
+    }
+  </script>
+  <body onload="runTest()"></body>
+</html>
diff --git a/dom/base/Document.cpp b/dom/base/Document.cpp
index c7f0a8966657..6385f57d75e3 100644
--- a/dom/base/Document.cpp
+++ b/dom/base/Document.cpp
@@ -11173,10 +11173,15 @@ bool Document::CanSavePresentation(nsIRequest* aNewRequest,
         ret = false;
       }
       if (manager->HasBeforeUnloadListeners()) {
-        MOZ_LOG(gPageCacheLog, mozilla::LogLevel::Verbose,
-                ("Save of %s blocked due to beforeUnload handlers", uri.get()));
-        aBFCacheCombo |= BFCacheStatus::BEFOREUNLOAD_LISTENER;
-        ret = false;
+        if (!mozilla::SessionHistoryInParent() ||
+            !StaticPrefs::
+                docshell_shistory_bfcache_ship_allow_beforeunload_listeners()) {
+          MOZ_LOG(
+              gPageCacheLog, mozilla::LogLevel::Verbose,
+              ("Save of %s blocked due to beforeUnload handlers", uri.get()));
+          aBFCacheCombo |= BFCacheStatus::BEFOREUNLOAD_LISTENER;
+          ret = false;
+        }
       }
     }
   }
diff --git a/dom/base/nsGlobalWindowInner.cpp b/dom/base/nsGlobalWindowInner.cpp
index 9deca8cf0087..c5700544ed53 100644
--- a/dom/base/nsGlobalWindowInner.cpp
+++ b/dom/base/nsGlobalWindowInner.cpp
@@ -81,6 +81,7 @@
 #include "mozilla/SpinEventLoopUntil.h"
 #include "mozilla/Sprintf.h"
 #include "mozilla/StaticPrefs_browser.h"
+#include "mozilla/StaticPrefs_docshell.h"
 #include "mozilla/StaticPrefs_dom.h"
 #include "mozilla/StaticPrefs_privacy.h"
 #include "mozilla/StorageAccess.h"
@@ -6590,13 +6591,22 @@ void nsGlobalWindowInner::EventListenerAdded(nsAtom* aType) {
     mHasVRDisplayActivateEvents = true;
   }
 
-  if ((aType == nsGkAtoms::onunload || aType == nsGkAtoms::onbeforeunload) &&
-      mWindowGlobalChild) {
+  if (aType == nsGkAtoms::onunload && mWindowGlobalChild) {
     if (++mUnloadOrBeforeUnloadListenerCount == 1) {
       mWindowGlobalChild->BlockBFCacheFor(BFCacheStatus::UNLOAD_LISTENER);
     }
-    if (aType == nsGkAtoms::onbeforeunload &&
-        (!mDoc || !(mDoc->GetSandboxFlags() & SANDBOXED_MODALS))) {
+  }
+
+  if (aType == nsGkAtoms::onbeforeunload && mWindowGlobalChild) {
+    if (!mozilla::SessionHistoryInParent() ||
+        !StaticPrefs::
+            docshell_shistory_bfcache_ship_allow_beforeunload_listeners()) {
+      if (++mUnloadOrBeforeUnloadListenerCount == 1) {
+        mWindowGlobalChild->BlockBFCacheFor(
+            BFCacheStatus::BEFOREUNLOAD_LISTENER);
+      }
+    }
+    if (!mDoc || !(mDoc->GetSandboxFlags() & SANDBOXED_MODALS)) {
       mWindowGlobalChild->BeforeUnloadAdded();
       MOZ_ASSERT(mWindowGlobalChild->BeforeUnloadListeners() > 0);
     }
@@ -6618,14 +6628,23 @@ void nsGlobalWindowInner::EventListenerAdded(nsAtom* aType) {
 }
 
 void nsGlobalWindowInner::EventListenerRemoved(nsAtom* aType) {
-  if ((aType == nsGkAtoms::onunload || aType == nsGkAtoms::onbeforeunload) &&
-      mWindowGlobalChild) {
+  if (aType == nsGkAtoms::onunload && mWindowGlobalChild) {
     MOZ_ASSERT(mUnloadOrBeforeUnloadListenerCount > 0);
     if (--mUnloadOrBeforeUnloadListenerCount == 0) {
       mWindowGlobalChild->UnblockBFCacheFor(BFCacheStatus::UNLOAD_LISTENER);
     }
-    if (aType == nsGkAtoms::onbeforeunload &&
-        (!mDoc || !(mDoc->GetSandboxFlags() & SANDBOXED_MODALS))) {
+  }
+
+  if (aType == nsGkAtoms::onbeforeunload && mWindowGlobalChild) {
+    if (!mozilla::SessionHistoryInParent() ||
+        !StaticPrefs::
+            docshell_shistory_bfcache_ship_allow_beforeunload_listeners()) {
+      if (--mUnloadOrBeforeUnloadListenerCount == 0) {
+        mWindowGlobalChild->UnblockBFCacheFor(
+            BFCacheStatus::BEFOREUNLOAD_LISTENER);
+      }
+    }
+    if (!mDoc || !(mDoc->GetSandboxFlags() & SANDBOXED_MODALS)) {
       mWindowGlobalChild->BeforeUnloadRemoved();
       MOZ_ASSERT(mWindowGlobalChild->BeforeUnloadListeners() >= 0);
     }
diff --git a/dom/base/nsGlobalWindowInner.h b/dom/base/nsGlobalWindowInner.h
index c3c29b90696a..e916a553d016 100644
--- a/dom/base/nsGlobalWindowInner.h
+++ b/dom/base/nsGlobalWindowInner.h
@@ -1520,7 +1520,7 @@ class nsGlobalWindowInner final : public mozilla::dom::EventTarget,
 
   RefPtr<mozilla::dom::VREventObserver> mVREventObserver;
 
-  // The number of unload and beforeunload even listeners registered on this
+  // The number of unload and beforeunload event listeners registered on this
   // window.
   uint64_t mUnloadOrBeforeUnloadListenerCount = 0;
 
diff --git a/dom/ipc/WindowGlobalParent.cpp b/dom/ipc/WindowGlobalParent.cpp
index 1cc0787ad633..289759230a74 100644
--- a/dom/ipc/WindowGlobalParent.cpp
+++ b/dom/ipc/WindowGlobalParent.cpp
@@ -1388,6 +1388,7 @@ nsCString BFCacheStatusToString(uint32_t aFlags) {
   ADD_BFCACHESTATUS_TO_STRING(HAS_USED_VR);
   ADD_BFCACHESTATUS_TO_STRING(CONTAINS_REMOTE_SUBFRAMES);
   ADD_BFCACHESTATUS_TO_STRING(NOT_ONLY_TOPLEVEL_IN_BCG);
+  ADD_BFCACHESTATUS_TO_STRING(BEFOREUNLOAD_LISTENER);
   ADD_BFCACHESTATUS_TO_STRING(ACTIVE_LOCK);
 
 #undef ADD_BFCACHESTATUS_TO_STRING
diff --git a/dom/tests/browser/browser_hasbeforeunload.js b/dom/tests/browser/browser_hasbeforeunload.js
index b9ef812d6ddf..97cd96aeaf0d 100644
--- a/dom/tests/browser/browser_hasbeforeunload.js
+++ b/dom/tests/browser/browser_hasbeforeunload.js
@@ -408,6 +408,12 @@ function assertHasBeforeUnload(browser, expected) {
  * inner window is removed from the DOM.
  */
 add_task(async function test_inner_window_scenarios() {
+  // Turn this off because the test expects the page to be not bfcached.
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["docshell.shistory.bfcache.ship_allow_beforeunload_listeners", false],
+    ],
+  });
   await BrowserTestUtils.withNewTab(
     {
       gBrowser,
@@ -592,6 +598,12 @@ add_task(async function test_inner_window_scenarios() {
  * to the iframe DOM nodes instead of the inner windows.
  */
 add_task(async function test_outer_window_scenarios() {
+  // Turn this off because the test expects the page to be not bfcached.
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["docshell.shistory.bfcache.ship_allow_beforeunload_listeners", false],
+    ],
+  });
   await BrowserTestUtils.withNewTab(
     {
       gBrowser,
@@ -787,6 +799,12 @@ add_task(async function test_outer_window_scenarios() {
  * are added on both inner and outer windows.
  */
 add_task(async function test_mixed_inner_and_outer_window_scenarios() {
+  // Turn this off because the test expects the page to be not bfcached.
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["docshell.shistory.bfcache.ship_allow_beforeunload_listeners", false],
+    ],
+  });
   await BrowserTestUtils.withNewTab(
     {
       gBrowser,
diff --git a/modules/libpref/init/StaticPrefList.yaml b/modules/libpref/init/StaticPrefList.yaml
index 63506081fff3..a19cae0a86c2 100644
--- a/modules/libpref/init/StaticPrefList.yaml
+++ b/modules/libpref/init/StaticPrefList.yaml
@@ -1816,6 +1816,13 @@
   value: @IS_ANDROID@
   mirror: always
 
+# If true, page with beforeunload event listeners can be bfcached.
+# This only works when sessionHistoryInParent is enabled.
+- name: docshell.shistory.bfcache.ship_allow_beforeunload_listeners
+  type: bool
+  value: @IS_NIGHTLY_BUILD@
+  mirror: always
+
 #---------------------------------------------------------------------------
 # Prefs starting with "dom."
 #---------------------------------------------------------------------------
diff --git a/testing/web-platform/meta/html/browsers/browsing-the-web/back-forward-cache/events.html.ini b/testing/web-platform/meta/html/browsers/browsing-the-web/back-forward-cache/events.html.ini
index f98bff68a2c6..3b9979f1026c 100644
--- a/testing/web-platform/meta/html/browsers/browsing-the-web/back-forward-cache/events.html.ini
+++ b/testing/web-platform/meta/html/browsers/browsing-the-web/back-forward-cache/events.html.ini
@@ -1,9 +1,8 @@
 [events.html]
+  prefs: [docshell.shistory.bfcache.ship_allow_beforeunload_listeners:true]
   [beforeunload]
     expected:
-      if os == "android": PASS
-      PRECONDITION_FAILED
-
+      if not sessionHistoryInParent and (os != "android") : PRECONDITION_FAILED
   [unload]
     expected:
       if os == "android": PASS
diff --git a/toolkit/components/remotebrowserutils/tests/browser/dummy_page.html b/toolkit/components/remotebrowserutils/tests/browser/dummy_page.html
index 907113cd1d66..8205e90d5dea 100644
--- a/toolkit/components/remotebrowserutils/tests/browser/dummy_page.html
+++ b/toolkit/components/remotebrowserutils/tests/browser/dummy_page.html
@@ -7,9 +7,7 @@
     <script>
         // Prevent this page from being stored in the bfcache for the
         // browser_httpToFileHistory.js test
-        window.addEventListener('beforeunload', event => {
-            // do nothing
-        });
+        window.blockBFCache = new RTCPeerConnection();
     </script>
 </body>
 </html>