chore(deps): update dependency zen-browser/desktop to v1.21.15b

[renovate]

This PR contains the following updates:

Package	Update	Change
zen-browser/desktop	patch	1.21.14b → 1.21.15b

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Release Notes

zen-browser/desktop (zen-browser/desktop)

v1.21.15b: Release build - 1.21.15b (2026-08-18)

Compare Source

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)
• Fix multiple glance tabs when joining tabs (#​14975)
• Improved rendering performance on MacOS and memory leaks when using WebRTC (#​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.

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