diff --git a/dom/fs/parent/datamodel/FileSystemDatabaseManagerVersion001.cpp b/dom/fs/parent/datamodel/FileSystemDatabaseManagerVersion001.cpp
index c65bf0150836..a898f1afb61c 100644
--- a/dom/fs/parent/datamodel/FileSystemDatabaseManagerVersion001.cpp
+++ b/dom/fs/parent/datamodel/FileSystemDatabaseManagerVersion001.cpp
@@ -1233,7 +1233,7 @@ void FileSystemDatabaseManagerVersion001::DecreaseCachedQuotaUsage(
 }
 
 nsresult FileSystemDatabaseManagerVersion001::UpdateCachedQuotaUsage(
-    const FileId& aFileId, Usage aOldUsage, Usage aNewUsage) {
+    const FileId& aFileId, Usage aOldUsage, Usage aNewUsage) const {
   quota::QuotaManager* quotaManager = quota::QuotaManager::Get();
   MOZ_ASSERT(quotaManager);
 
diff --git a/dom/fs/parent/datamodel/FileSystemDatabaseManagerVersion001.h b/dom/fs/parent/datamodel/FileSystemDatabaseManagerVersion001.h
index 333c5af6c259..64ecfa5b01c9 100644
--- a/dom/fs/parent/datamodel/FileSystemDatabaseManagerVersion001.h
+++ b/dom/fs/parent/datamodel/FileSystemDatabaseManagerVersion001.h
@@ -130,7 +130,7 @@ class FileSystemDatabaseManagerVersion001 : public FileSystemDatabaseManager {
   void DecreaseCachedQuotaUsage(int64_t aDelta);
 
   nsresult UpdateCachedQuotaUsage(const FileId& aFileId, Usage aOldUsage,
-                                  Usage aNewUsage);
+                                  Usage aNewUsage) const;
 
   nsresult ClearDestinationIfNotLocked(
       const FileSystemConnection& aConnection,
diff --git a/dom/fs/parent/datamodel/FileSystemDatabaseManagerVersion002.cpp b/dom/fs/parent/datamodel/FileSystemDatabaseManagerVersion002.cpp
index 3543346ff071..a6c61b0e3e26 100644
--- a/dom/fs/parent/datamodel/FileSystemDatabaseManagerVersion002.cpp
+++ b/dom/fs/parent/datamodel/FileSystemDatabaseManagerVersion002.cpp
@@ -463,6 +463,9 @@ nsresult FileSystemDatabaseManagerVersion002::GetFile(
     if (mainFileId) {
       QM_TRY_UNWRAP(aFile,
                     mFileManager->CreateFileFrom(aFileId, mainFileId.value()));
+      int64_t fileSize = 0;
+      QM_TRY(QM_TO_RESULT(aFile->GetFileSize(&fileSize)));
+      UpdateCachedQuotaUsage(aFileId, 0, fileSize);
     } else {
       // LockShared/EnsureTemporaryFileId has provided a brand new fileId.
       QM_TRY_UNWRAP(aFile, mFileManager->GetOrCreateFile(aFileId));
diff --git a/dom/fs/test/common/test_writableFileStream.js b/dom/fs/test/common/test_writableFileStream.js
index 016c53bf3b00..5b6caa0d2057 100644
--- a/dom/fs/test/common/test_writableFileStream.js
+++ b/dom/fs/test/common/test_writableFileStream.js
@@ -2,6 +2,7 @@
    http://creativecommons.org/publicdomain/zero/1.0/ */
 
 const allowCreate = { create: true };
+const denyCreate = { create: false };
 
 exported_symbols.test0 = async function () {
   let root = await navigator.storage.getDirectory();
@@ -145,6 +146,111 @@ exported_symbols.bug1825018 = async function () {
   }
 };
 
+exported_symbols.usageTest = async function () {
+  const bufferSize = 1024;
+  const keepData = { keepExistingData: true };
+  const fromEmpty = { keepExistingData: false };
+
+  let root = await navigator.storage.getDirectory();
+  Assert.ok(root, "Can we access the root directory?");
+
+  const baseUsage = await Utils.getCachedOriginUsage();
+  Assert.ok(true, "Usage " + baseUsage);
+  // Create a file.
+  {
+    const fileHandle = await root.getFileHandle("usagetest.txt", allowCreate);
+    Assert.ok(!!fileHandle, "Can we get file handle?");
+
+    const writable = await fileHandle.createWritable(fromEmpty);
+    Assert.ok(!!writable, "Can we create writable file stream?");
+
+    const buffer = new ArrayBuffer(bufferSize);
+    Assert.ok(!!buffer, "Can we create array buffer?");
+
+    const result = await writable.write(buffer);
+    Assert.equal(result, undefined, "Can we write entire buffer?");
+
+    await writable.close();
+  }
+
+  {
+    const fileUsage = await Utils.getCachedOriginUsage();
+    Assert.ok(true, "Usage " + fileUsage);
+    Assert.ok(fileUsage >= baseUsage + bufferSize);
+
+    const fileHandle = await root.getFileHandle("usagetest.txt", denyCreate);
+    Assert.ok(!!fileHandle, "Can we get file handle?");
+
+    {
+      const usageNow = await Utils.getCachedOriginUsage();
+      Assert.equal(usageNow, fileUsage);
+    }
+
+    const writableA = await fileHandle.createWritable(keepData);
+    Assert.ok(!!writableA, "Can we create writable file stream?");
+
+    {
+      const usageNow = await Utils.getCachedOriginUsage();
+      Assert.ok(true, "Usage " + usageNow.usage);
+      Assert.equal(usageNow, fileUsage + bufferSize);
+    }
+
+    const writableB = await fileHandle.createWritable(keepData);
+    Assert.ok(!!writableB, "Can we create writable file stream?");
+
+    {
+      const usageNow = await Utils.getCachedOriginUsage();
+      Assert.equal(usageNow, fileUsage + 2 * bufferSize);
+    }
+
+    const writableC = await fileHandle.createWritable(keepData);
+    Assert.ok(!!writableC, "Can we create writable file stream?");
+
+    {
+      const usageNow = await Utils.getCachedOriginUsage();
+      Assert.equal(usageNow, fileUsage + 3 * bufferSize);
+    }
+
+    const writableD = await fileHandle.createWritable(fromEmpty);
+    Assert.ok(!!writableD, "Can we create writable file stream?");
+
+    {
+      const usageNow = await Utils.getCachedOriginUsage();
+      // We did not keep existing data for this writable
+      Assert.equal(usageNow, fileUsage + 3 * bufferSize);
+    }
+
+    await writableA.abort();
+
+    {
+      const usageNow = await Utils.getCachedOriginUsage();
+      Assert.equal(usageNow, fileUsage + 2 * bufferSize);
+    }
+
+    await writableB.close();
+
+    {
+      const usageNow = await Utils.getCachedOriginUsage();
+      Assert.equal(usageNow, fileUsage + bufferSize);
+    }
+
+    await writableC.abort();
+
+    {
+      const usageNow = await Utils.getCachedOriginUsage();
+      Assert.equal(usageNow, fileUsage);
+    }
+
+    await writableD.close();
+
+    {
+      const usageNow = await Utils.getCachedOriginUsage();
+      // Buffer was overwritten with nothing.
+      Assert.equal(usageNow, fileUsage - bufferSize);
+    }
+  }
+};
+
 for (const [key, value] of Object.entries(exported_symbols)) {
   Object.defineProperty(value, "name", {
     value: key,