Zen Browser 1.23b Adds "Library" and Ships on Firefox 157
Zen Browser 1.23b is out, and the headline feature is a new hub called Library, which the team describes as "a better place to organize and access your history, media, downloads, spaces and more." It's built on Firefox 157.0, landed on GitHub between October 1 and 2, 2026, and yes, it patches more than 70 browser vulnerabilities. For an independent browser running on a core team measured in single digits, that's a lot of ground to cover.
The release is the latest in what has become a relentless cadence for the project. Zen has been shipping updates roughly every one to two weeks throughout 2026, each stacked on top of the current Firefox release. There's a stable channel and an experimental "Twilight" channel for people who like living on the edge. The numbered "b" builds, like this one, are what the team actually recommends you install.
What Library actually does
Here's the honest read: Zen hasn't published full documentation on Library yet, so we're working off the framing alone. It sounds like a consolidated panel that pulls together browsing history, embedded media, downloaded files, and Spaces, pieces of data that were previously scattered across separate menus, into one navigable spot.
That's squarely in line with Zen's whole design ethos: cut the clutter, keep productivity tools reachable. If you hoard tabs across half a dozen named workspaces and lose track of what you downloaded last week, this is the feature aimed at you.
The other concrete additions are more tangible. Hardware-accelerated AV1 decoding for WebRTC video calls is now in, meaning Google Meet, Zoom's web client, and friends stop chewing through your CPU on capable devices. Previously Zen decoded everything in software, which drains laptop batteries in a matter of hours. If your machine supports AV1 hardware decoding, you'll feel the difference.
There's also a tweak to the auto-hiding sidebar: you can now resize it below the threshold at which it hides itself, so it behaves more intuitively in Compact Mode and leaves your screen maximally clear when you're not using it.
The stuff that matters most
Let's be straight about which part of this release you should actually care about. It's the security patching.
Zen inherits Mozilla's Firefox 157 advisory: MFSA2026-97, dated September 29, 2026, rated high impact. Mozilla changed its publishing approach here, so instead of lumping memory-safety bugs into one bucket, it issued findings individually. Firefox 157 alone enumerates more than 70 CVEs, the large majority rated "high." The classes are the usual suspects from the modern browser threat playbook: use-after-free across Graphics/WebGPU, DOM, JavaScript/WebAssembly, and Networking; sandbox escapes that let malicious pages break out of isolation; privilege escalation; same-origin policy bypasses in WebExtensions and DevTools; and information disclosure over the JAR protocol and in general Networking components.
Mozilla credited reporters from OpenAI, Tencent KeenLab, and several independent researchers, alongside its own internal findings.
The upshot is simple. These bugs are fixed in the Firefox 157 engine that Zen 1.23b is built on, so running anything older leaves you exposed to actively exploitable issues that can lead to remote code execution. Upgrading isn't optional here.
It's a rather security-heavy release for a "what's new" announcement, which says something about where browser development has landed. But the productivity tweaks are real too, even if Library itself needs a bit more explanation to land fully.
A little polish, a lot of commits
Beyond features, 1.23b quietly fixes a bunch of things that quietly annoy people. Startup performance with lots of tabs open got a notable boost, the window-creation-and-tab-restoration slog that power users loathe. Icon animations for the boost indicator and media player musical notes in the sidebar are smoother now (GitHub #15299). The status panel and Glance controls finally use the correct theme colors, which matters most if you're on a custom theme or dark mode.
On Windows, some 8-bit HDR videos that previously looked dull and gray now render correctly, and full-screen video no longer leaves the taskbar parked on top of it. Audio-video sync during playback-speed changes also improved, which is a small mercy for everyone who's ever watched a lecture at 2x and lost the lip-sync.
Behaviorally, a few niceties: links routed to a Space now prefer the window that already has that space open instead of spawning another one; the sidebar and command bar get blur effects; macOS sidebar buttons grew larger for better touch targets; a right-swipe on your last space creates a new one; and the bottom buttons flip when the sidebar sits on the right.
Should you update?
Yes, for most people. Three reasons stack up.
Security is the obvious one, it fixes 70+ vulnerabilities, many high-impact and exploitable. Library is the productivity pull, especially if you juggle heavy history, downloads, media, and Spaces. And the performance fixes includes multi-tab startup, hardware AV1 decoding, smoother animations, which hit the day-to-day experience most directly on laptops and lower-power machines.
If you'd rather wait, keep in mind that Zen's cadence means the next update is likely only weeks away. There's little downside to taking 1.23b now, particularly given how much of it is security.
Where to get it
Zen Browser 1.23b is available today for macOS, Windows, and Linux, including ARM64 builds for Mac and PC, plus a Flathub package for Linux users. It's still in beta, distributed free, and released under the Mozilla Public License v2, with no ads, telemetry, subscriptions, or account requirements, though an optional Mozilla account unlocks cross-device sync.
You can grab the stable build from here, or head to the GitHub releases page for the direct link. Bug reports live on the project's GitHub Issues, feature requests on GitHub Discussions, and donations (the team runs on community effort and sponsorships from partners like BlackSmith and Crowdin) are collected at zen-browser.app/donate.
