diff --git a/testing/web-platform/mozilla/meta/dom/fs/__dir__.ini b/testing/web-platform/mozilla/meta/dom/fs/__dir__.ini
new file mode 100644
index 0000000000000..2718527bf8e87
--- /dev/null
+++ b/testing/web-platform/mozilla/meta/dom/fs/__dir__.ini
@@ -0,0 +1 @@
+leak-threshold: [default:51200]
diff --git a/testing/web-platform/mozilla/meta/dom/fs/fs-writable_unlocked_on_tab_close.https.window.js.ini b/testing/web-platform/mozilla/meta/dom/fs/fs-writable_unlocked_on_tab_close.https.window.js.ini
new file mode 100644
index 0000000000000..2174a08ddbc0a
--- /dev/null
+++ b/testing/web-platform/mozilla/meta/dom/fs/fs-writable_unlocked_on_tab_close.https.window.js.ini
@@ -0,0 +1,5 @@
+[fs-writable_unlocked_on_tab_close.https.window.html]
+ type: testharness
+ prefs:
+ [dom.storageManager.enabled:true,
+ dom.fs.enabled:true]
diff --git a/testing/web-platform/mozilla/tests/dom/fs/fs-writable_unlocked_on_tab_close.https.window.js b/testing/web-platform/mozilla/tests/dom/fs/fs-writable_unlocked_on_tab_close.https.window.js
new file mode 100644
index 0000000000000..6e8192aaefc63
--- /dev/null
+++ b/testing/web-platform/mozilla/tests/dom/fs/fs-writable_unlocked_on_tab_close.https.window.js
@@ -0,0 +1,70 @@
+// META: title=Origin private file system used from multiple tabs
+// META: script=support/testHelpers.js
+
+promise_test(async t => {
+ const bc = new BroadcastChannel("Coordinate writables");
+
+ function firstReady(win) {
+ return new Promise(resolve => {
+ // Blur triggers after the unload event and after window.closed is set
+ win.onblur = () => {
+ // Closing the low-level file handle may get stuck, but the unlocking
+ // request can only be sent to the parent after the handle is closed.
+ // There is no guarantee when or if the closing will be complete.
+ //
+ // Therefore, the content process shutdown does not wait for the
+ // completion but sets window.closed and calls the unload listeners
+ // while actually still holding onto some resources.
+ //
+ // Since in this test we mainly want to ensure that a file
+ // does not remain locked indefinitely, we wait for a reasonable amount
+ // of time before creating a new writable, corresponding roughly to
+ // a 500ms closing delay.
+ const timeoutMs = 400;
+ setTimeout(() => {
+ resolve(win);
+ }, timeoutMs);
+ };
+ });
+ }
+
+ const firstTabName = "support/fs-open_writable_then_close_tab.sub.html";
+ const firstTab = await firstReady(window.open(firstTabName));
+ assert_true(firstTab.closed, "Is the first tab already closed?");
+
+ function secondReady(win) {
+ return new Promise(resolve => {
+ bc.onmessage = e => {
+ if (e.data === "Second window ready!") {
+ resolve(win);
+ }
+ };
+ });
+ }
+
+ const secondTabName = "support/fs-open_writable_after_trigger.sub.html";
+ const secondTab = await secondReady(window.open(secondTabName));
+
+ let isDone = false;
+ let childStatus = "Success";
+
+ const secondSucceeded = new Promise(resolve => {
+ bc.onmessage = e => {
+ isDone = true;
+ if (e.data !== "Success") {
+ childStatus = e.data;
+ }
+
+ resolve();
+ };
+ });
+
+ bc.postMessage("Create writable in the second window");
+
+ await secondSucceeded;
+ assert_true(isDone, "Did the second tab respond?");
+
+ await fetch_tests_from_window(secondTab);
+
+ assert_equals(childStatus, "Success");
+}, `writable available for other tabs after one tab is closed`);
diff --git a/testing/web-platform/mozilla/tests/dom/fs/support/fs-open_writable_after_trigger.sub.html b/testing/web-platform/mozilla/tests/dom/fs/support/fs-open_writable_after_trigger.sub.html
new file mode 100644
index 0000000000000..b64d97083f592
--- /dev/null
+++ b/testing/web-platform/mozilla/tests/dom/fs/support/fs-open_writable_after_trigger.sub.html
@@ -0,0 +1,45 @@
+
+
+Child context test(s)
+
+
+
+
+
+
+
+
+
diff --git a/testing/web-platform/mozilla/tests/dom/fs/support/fs-open_writable_then_close_tab.sub.html b/testing/web-platform/mozilla/tests/dom/fs/support/fs-open_writable_then_close_tab.sub.html
new file mode 100644
index 0000000000000..098fe83b1f8e6
--- /dev/null
+++ b/testing/web-platform/mozilla/tests/dom/fs/support/fs-open_writable_then_close_tab.sub.html
@@ -0,0 +1,20 @@
+
+
+Child context test(s)
+
+
+
+
+
+
+
+
diff --git a/testing/web-platform/mozilla/tests/dom/fs/support/testHelpers.js b/testing/web-platform/mozilla/tests/dom/fs/support/testHelpers.js
new file mode 100644
index 0000000000000..5cf47435c1a50
--- /dev/null
+++ b/testing/web-platform/mozilla/tests/dom/fs/support/testHelpers.js
@@ -0,0 +1,15 @@
+async function waitUntil(isWaitDone, untilMs, stepMs = 25) {
+ const startMs = Date.now();
+
+ return new Promise((resolve, reject) => {
+ const areWeDoneYet = setInterval(async function() {
+ if (await isWaitDone()) {
+ clearInterval(areWeDoneYet);
+ resolve();
+ } else if (Date.now() > startMs + untilMs) {
+ clearInterval(areWeDoneYet);
+ reject(new Error("Timed out after " + untilMs + "ms"));
+ }
+ }, stepMs);
+ });
+}