Mellow

A calm, space-first Android browser that syncs with Zen Browser.

Mellow is a fork of WebLibre rebuilt around Zen Browser's data model — spaces, nested folders, essentials, a vertical rail — and wired into Zen's own spaces Firefox Sync engine, so the spaces you keep on the desktop are the spaces you get on the phone, in both directions.

Underneath it is still WebLibre's browser: Mozilla's Gecko engine driven through Mozilla Android Components, which is why pages render and Firefox extensions behave the way they do in Firefox for Android.

Note

This is a personal build. It exists because one person wanted Zen's spaces on their phone with extensions that work. There is no store listing, no roadmap and no support. It is not affiliated with, endorsed by or supported by WebLibre, OnDevice UG, Zen Browser or Mozilla. If you want a maintained privacy browser, go and use WebLibre — it is the better-tested software and it is where this one came from.

What it does

• Zen spaces, two ways. A Sync 1.5 client for Zen's spaces collection (engine version 3): spaces, their order, icons, theme and pinned-tab containers round-trip with the desktop. Local state stays local, and the uploader is hardened against the tombstone bug that has eaten spaces upstream.
• The Zen shape. Spaces with nested folders and essentials, a wide vertical rail on tablets and unfolded screens, a compact bar on phones, and an optional slide-out rail that a back-edge swipe pulls in from either side.
• Extensions. Firefox-compatible WebExtensions, kept first-class. Everything else in this fork was judged against whether it got in the way of that or of sync.
• Firefox Sync for the rest. History, bookmarks and tabs over the same account.
• Less of everything else. Roughly 128k lines of upstream features were removed rather than carried — see what changed.

Status

Built and run daily on exactly one device (a Samsung foldable, Android 17). It is not tested anywhere else, on any other screen, or by anyone else. Treat everything here as "works for me".

Mellow has its own application id (app.mellow.browser), so it installs beside WebLibre rather than over it and never touches WebLibre's update channel.

APKs are on the releases page: arm64 only, Android 8.0+, signed with this project's own key. Every release note carries the APK's SHA-256. They are cut by hand from a local build (scripts/release.sh) rather than by CI, so that every build ever installed on a phone carries the same signature — Android refuses to update an app whose signing certificate changed.

Building

# Flutter 3.47.3, JDK 17, Android SDK
dart pub global activate melos
melos bootstrap
melos run update-assets      # downloads the external data files
melos run build-components   # builds the readability JS bundle
melos run build              # build_runner across the workspace

cd apps/mellow
flutter build apk --release --flavor alpha --split-per-abi \
  --target-platform android-arm64 --no-tree-shake-icons

build.gradle falls back to debug signing when KEY_PATH is unset, which is fine for a build you only install yourself and fatal for one you publish — so scripts/release.sh refuses to release an APK it finds debug-signed.

Credits

Mellow is other people's work with a different shape on top. In order of how much is owed:

• WebLibre by Fabian Freund / OnDevice UG — the browser. Engine integration, extensions, containers, the whole Flutter↔Android Components bridge, and the four plugin packages this repo still ships. AGPL-3.0-or-later; Mellow is a derivative work and stays under the same licence.
• Zen Browser — the spaces model and the sync record format Mellow speaks. No Zen code is copied here; the client was written against the behaviour of Zen's own sync engine so the two agree on the wire.
• Mozilla — GeckoView, Android Components and Firefox Sync, under MPL-2.0.

Full attribution, including the bundled third-party assets, is in NOTICE.

License

Mellow is free software under the GNU Affero General Public License v3.0 or later, inherited from WebLibre. Every source file keeps its original copyright header. Changes made in this fork are documented in docs/CHANGES-FROM-WEBLIBRE.md, as AGPL §5 asks.

The name Mellow and its icon are this fork's own. The names WebLibre, Zen Browser, Firefox and Mozilla belong to their owners and are used here only to say, factually, what this software is built on and talks to.