FileSystem

FileSystem Experiment (removed)

Important

This Experiment API has been removed. Use the VFS Toolkit instead.

The FileSystem Experiment was an interim solution which gave add-ons read/write access to a single folder inside the user's profile folder. That approach is obsolete.

Use the VFS Toolkit instead

The VFS Toolkit is part of this repository and is the recommended way for add-ons to read and write user files. It is a plain JavaScript module - no Experiment API needed.

The core idea is the Virtual File System (VFS) concept: your add-on works with plain absolute paths and never has to care where the files actually live. The user decides that, by installing and configuring the storage provider that suits their needs - which may well be their local home folder, if they choose to install that provider.

Storage backends currently available to the user:

Storage backend	Description
OPFS	Built into the VFS Toolkit. A virtual file system stored inside the user's profile, isolated per add-on. This is the closest equivalent to what the FileSystem Experiment used to provide.
Local Home Folder	Access files in the user's local home folder (via Native Messaging).
WebDAV	Access files directly on a WebDAV server, for example Nextcloud or ownCloud.
OneDrive	Access files stored in the user's Microsoft OneDrive account.

More providers (for example Nextcloud and Seafile) are on the way, and third parties can add their own through the Provider API. Your add-on does not need to be changed to support any of them.

On top of that, the VFS Toolkit ships a file picker UI, something Mozilla does not provide for OPFS.

Examples

Vendor the vfs-client module into your add-on and import it:

import * as vfs from '/vendor/vfs-toolkit/vfs-client/vfs-client.mjs';

// once, in your background script
vfs.init({
  enableExternalProviders: true,
  configStorageKey: "vfs-toolkit-config-data",
});

Reading and writing a file:

const file = await vfs.readFile({ path: "/notes.txt" });
const text = await file.text();

await vfs.writeFile(
  { path: "/notes.txt" },
  new Blob([text], { type: "text/plain" }),
  { overwrite: true }
);

Omitting storageRef (as above) targets the built-in OPFS backend. To let the user pick a location on any of their configured storages, use one of the pickers:

const [entry] = await vfs.showSelectFilePicker();
if (entry) {
  const file = await vfs.readFile(entry);
}

Documentation and examples

• VFS Toolkit overview
• Client API reference - all read/write/copy/move/delete methods, pickers, events and types
• Provider API reference - for implementing your own storage backend
• Example client add-on
• Example provider add-on