Zen Browser 1.21.16b

Zen is Firefox with the tab strip moved to the side and the clutter taken out.

Instead of fifty shrinking tabs along the top, you get vertical tabs in a sidebar, separate workspaces for work and personal browsing, and a split view that puts two pages side by side in one window.

Version 1.21.16b, published on 27 August 2026, is a small release with one line in it that matters more than the rest.

What Zen Browser Actually Does, in Plain Terms

Zen is Mozilla Firefox underneath. Same rendering engine, same extension support, same privacy foundation, wrapped in a completely rethought interface.

The toolbar and tab list sit on the left of the window, the main area splits into panes so you can compare several pages at once, and workspaces keep separate browsing sessions apart.

A compact mode hides nearly all the controls until you need them, which is why Zen screenshots look more like a reading app than a browser.

Two things you will not find in stock Firefox: Zen Mods, a built-in gallery of community themes and interface tweaks you install with one click, and Boosts, which apply custom styling to individual websites.

Because it inherits the Firefox engine, Zen plays modern web video exactly as Firefox does, including H.264 and VP9 streams on YouTube and similar sites.

AV1, the newer royalty-free codec those sites increasingly default to, decodes the same way, so there is nothing extra to install.

If a file will not play and you want to know whether the browser is the problem, our Web Player and HEVC Player run entirely in your browser and settle it in a few seconds.

What 1.21.16b Changes

This is a short list, but it is not the pure bugfix release the last two were, because the engine underneath moves forward with it.

• The engine moves to Firefox 154.0.1 Mozilla lists no security advisory against 154.0.1, so treat this as compatibility and stability work rather than a patch you need to install tonight.
• FFmpeg 63 is now supported. Firefox-based browsers use the system FFmpeg for part of their video decoding on Linux, and each new major version has to be recognised explicitly or playback falls back to slower software paths.
• Feature callouts use native panels. The little tips that introduce new features were drawing their own panel instead of the platform one, so they looked out of place against the rest of the interface.
• No more hang with one tab in two windows. Opening the same tab in two windows under different containers could lock the browser up, and that is fixed.

If you are coming from 1.21.12b or earlier, the repairs from the last two builds arrive with this one as well.

• Selecting text near the top of a page works again. The new window dragging was catching those clicks and moving the whole window instead of selecting, which was fixed in 1.21.12b.
• The sidebar no longer fills with duplicate media controls. Pages carrying several players were spawning them endlessly, and 1.21.13b stopped it.
• Restoring a closed pinned tab puts it back where it belongs. It returns to the pinned tabs container instead of landing loose among the ordinary tabs.

Further back again, 1.21.11b is the build worth knowing about, because it is where the features those repairs were fixing came from.

• Faster startup. Zen's slow cold start had been a standing complaint, and 1.21.11b worked on both the measured time and how quick it feels.
• Drag the window by the page itself. Grab empty space in the top part of a webpage and move the window with native snapping and tiling, just as if you had grabbed the titlebar.
• Compact mode follows your mouse out of the window. The sidebar stays open while the cursor lingers near the edge and only tucks away once you move properly clear - Windows and macOS only, Linux is unchanged.
• Several media controls at once. The sidebar can show more than one playing source, so you can pause a video in another tab without hunting for it.

Further back still, 1.21.10b is the build that finally made HDR video playback and NVIDIA RTX Super Resolution work on Windows, after both were announced with the Firefox 153 engine and did not function.

There is also a Twilight channel, a pre-release build where new work lands first, currently testing Spaces sync across devices through a Mozilla account. It is genuinely unfinished software and can break, so stay on the stable channel unless you enjoy filing bug reports.

Who Zen Browser Is For

People who keep dozens of tabs open and want structure: researchers, developers, students, anyone juggling several projects at once.

It is also a natural pick if you care about privacy but find stock Firefox visually dated. Our browser privacy roundup covers what each browser sends home.

Pairing it with a private search engine such as Qwant rounds out the setup, and The Open-Source Browser That Wants Your Attention, Not Your Data is a good companion read if the open-source angle is the draw.

Zen is also the closest maintained match for anyone leaving Arc Browser, which stopped active development in 2025. Workspaces, vertical tabs and split view all carry over conceptually.

If you are still deciding whether to move, what happened to the team behind it is the background worth having first.

Who Should Look Elsewhere

Zen does not support Widevine DRM, so protected streaming services including Netflix and HBO Max will not play. The licence carries costs and a corporate structure that are not feasible for an independent open-source project.

If streaming is part of your routine, keep Google Chrome or Microsoft Edge installed alongside Zen for those sites.

Note the "b" in the version number too. Zen still labels its stable channel as beta, and while it is reliable in daily use, the occasional rough edge is part of the deal, as the last three releases show.

Zen Browser vs Firefox, Brave and the Rest

Against stock Mozilla Firefox, Zen trades familiarity for organisation: same engine, same add-ons, radically different layout.

Against Brave Browser the split is engine philosophy. Brave is Chromium with aggressive built-in ad blocking, while Zen is Firefox with interface innovation and leans on extensions such as uBlock Origin.

If you are weighing Brave specifically, Is Brave Browser Still Worth It? digs into the trade-offs.

Opera Browser offers overlapping ideas such as a sidebar and workspaces, but it is closed source and Chromium-based.

Fellow Firefox forks LibreWolf and Floorp chase privacy and customisation from a different angle if Zen's layout is not for you.

The full lineup is in our web browsers section.

Before You Install

The Windows installer is roughly 92 MB, with separate x64 and ARM64 builds. Pick ARM64 only for Snapdragon-based laptops.

Zen runs on Windows 10 and 11, macOS and Linux. Your Firefox profile does not always migrate on its own, but the import wizard pulls bookmarks, passwords and history from Firefox, Chrome and Edge on first launch.

Expect a short adjustment period. Keyboard-driven features such as Glance, which peeks at a link without leaving the page, and workspace switching pay off after a day or two of muscle memory.

Quick questions

Download Zen Browser 1.21.16b and see how it handles your tabs, or tell us how you got on if you have used it before.