# Zen Browser 1.21.15b — Release build - 1.21.15b (2026-08-18)

- Product: Zen Browser (https://whatsnew.fyi/product/zen-browser)
- Vendor: Zen Browser
- Date: 2026-08-19
- Version: 1.21.15b
- Original notes: https://github.com/zen-browser/desktop/releases/tag/1.21.15b
- Permalink: https://whatsnew.fyi/product/zen-browser/releases/1.21.15b

What's New is an index, not a publisher: every entry below links to the vendor's own release notes, which are the authoritative source. Entries are labelled where they are hand-curated sample data, pre-releases, or drawn from a secondary source such as a developer blog.

Reuse: the summaries, labels and curation here are © What's New. Quote freely with attribution and a link back; wholesale republication of the corpus is not permitted — terms: https://whatsnew.fyi/terms. The vendors' own release notes remain their publishers'.

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- **security** — Address security advisories from Mozilla Firefox
- **changed** — Update Firefox version to 154.0
- **added** — Local Zen profile backups are now available on macOS in addition to Windows and Linux, and backups can be restored across all three platforms
- **added** — Sites can now be exempted from having their cookies and site data cleared on shutdown without also being exempted from tracking protection and other cookie restrictions
- **added** — The full-page Translations feature now translates iframe content
- **changed** — The full-page Translations feature now runs language identification on all page loads
- **changed** — Performing a hard reload on a page now also clears and updates its cached favicons
- **fixed** — Improved battery life on macOS when using vibrancy effects
- **fixed** — Improved performance of session restore by reducing CPU usage spikes when storing session to disk
- **fixed** — Fix multiple glance tabs when joining tabs
- **fixed** — Improved rendering performance on macOS and reduced memory leaks when using WebRTC
- **fixed** — Fixed an issue on macOS where closing a browser window could leave behind an invisible window that continued to capture mouse clicks
- **fixed** — Fixed an issue on Windows where an auto-hiding taskbar would not appear until the Zen window had been minimized and restored after launch
- **fixed** — Fixed an issue where the Windows taskbar would appear in front of a full screen Picture-in-Picture window
- **fixed** — Fixed PDF documents not being scaled correctly in print preview when the Fit to Page Width option is used

#### Zen Stable Release


##### Security
- https://www.mozilla.org/en-US/security/advisories/mfsa2026-74/

##### New Features
- Update Firefox version to 154.0
- Local Zen profile backups are now available on macOS in addition to Windows and Linux, and backups can be restored across all three platforms.
- Sites can now be exempted from having their cookies and site data cleared on shutdown without also being exempted from tracking protection and other cookie restrictions.
- The full-page Translations feature now translates <iframe> content.
- The full-page Translations feature now runs language identification on all page loads, resulting in an improved experience for offering translations to users.
- Performing a hard reload on a page (holding Shift while clicking the Refresh button) now also clears and updates its cached favicons.

##### Fixes
- Improved battery life on MacOS when using vibrancy effects
- Improved performance of session restore, having spikes of CPU usage every time the session is stored into disk ([#14990](https://github.com/zen-browser/desktop/issues/14990))
- Fix multiple glance tabs when joining tabs ([#14975](https://github.com/zen-browser/desktop/issues/14975))
- Improved rendering performance on MacOS and memory leaks when using WebRTC ([#9649](https://github.com/zen-browser/desktop/issues/9649))
- Fixed an issue on macOS where closing a browser window could leave behind an invisible window that continued to capture mouse clicks over the area where it used to be.
- Fixed an issue on Windows where an auto-hiding taskbar would not appear until the Zen window had been minimized and restored after launch.
- Fixed an issue where the Windows taskbar would appear in front of a full screen Picture-in-Picture window.
- Fixed PDF documents not being scaled correctly in print preview when the Fit to Page Width option is used.
- Other bug fixes and improvements.

##### Known Issues
- Following recent changes to Zen's password storage, some users may experience slower performance when Zen accesses saved passwords. Users with a Primary Password enabled may also see unexpected password prompts, such as when starting Zen or opening certain content.