Zen Browser has released version 1.21.4b, updating its Gecko engine to Firefox 152.0.2 and 152.0.3. The stable release introduces direct URL editing for pinned tabs and a quick context menu option to add domains to Space Routing. Users will also notice fixes for sidebar flicker when moving tabs, improved full-screening behavior for glance previews, and corrected foreground routing logic. The update continues the project's push to deliver an Arc-inspired, non-Chromium browsing experience built on Mozilla's open-source engine.

Zen Browser 1.21.4b Released with Firefox 152 Engine Bumps and Pinned Tab Edits

The Arc-inspired Firefox fork updates its stable release with space routing shortcuts, pinned tab fixes, and a sidebar flicker patch.

Zen Browser has released version 1.21.4b, the latest stable update for its Arc-inspired Firefox fork. The release bumps the engine to Firefox 152.0.2 and 152.0.3 while adding targeted tweaks for tab management and space routing.

Zen continues to carve a path for users who want the vertical tab productivity of Arc without the Chromium ecosystem. Since its first release in July 2024, the project has grown fast. When The Browser Company announced Arc would stop receiving new features, Zen positioned itself as a major alternative. It currently sits at around 43.1k GitHub stars, proving there's real demand for a customizable, Gecko-based alternative that feels modern.

Key changes in 1.21.4b

The 'Edit pinned tab' context menu item lets you manually set a URL for a pinned tab without unpinning it first. You can right-click the tab and change the address directly. It saves a click and stops the flow.

If you use Space Routing, Zen has added 'Add Route for Domain' to the context menu. You can now quickly add a tab's domain to your routing settings from the browser. No hunting through menus.

Under the hood, the update updates the base to Firefox 152.0.2 and 152.0.3. That brings the security patches and Gecko improvements you'd expect.

The release also clears up a few annoyances. Sidebar flicker fixed. Moving tabs no longer triggers sidebar flickering, resolving issue #14131. Full-screening a glance tab now expands it to a normal tab instead of leaving it stuck in preview mode. And finally, a fix for space routing tabs opening in the background when they should be in the foreground.

For what it's worth, Zen remains one of the most ambitious forks of Firefox. The project's reliance on Mozilla's engine means you get the freedom of the MPL-2.0 license with the stability of Firefox updates. You also get all standard Firefox extensions working out of the box.

Head to zen-browser.app to download the update. The source code is available on GitHub under zen-browser/desktop.