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Desktop
August 19, 2025

6.6.0 - Major ESR 140 upgrade with vertical tabs, tab groups, and new tab experience

Waterfox 6.6.0 is a major release that upgrades the underlying platform from 128.0 to 140.0 and delivers first‑party vertical tabs, private tabs in the same window, tab grouping, new‑tab wallpapers, expanded media and hardware acceleration, and sensible privacy defaults. This final release rolls up all changes from the beta series and includes stability and polish fixes.

Highlights

  • Vertical Tabs with optional Tree view
  • Private Tab button next to New Tab
  • Automatic Tab Grouping (configurable)
  • New Tab wallpapers, optional search bar and weather
  • Firefox profile import (bookmarks, history, passwords, cookies, form data)
  • WebGPU enabled; VP8/VP9 hardware acceleration for WebRTC
  • JPEG XL support; improved MathML rendering
  • Privacy‑friendly defaults (less promos, fewer speculative/remote fetches)
  • Numerous UI refinements and performance improvements

New

Tabs & Sidebar

  • Vertical Tabs: First‑party vertical tabstrip integrated into the sidebar, with customization options.
  • Tree‑Style Vertical Tabs: Optional tree layout for vertical tabs.
    • How to enable: Show sidebar → Customize sidebar → Sidebar settings → Vertical tabs → Tree vertical tabs.
  • Private Tab Button: Quick “New Private Tab” button next to the New Tab button.
  • Automatic Tab Grouping: New tabs can automatically open within your existing tab groups for a more organized session.
    • Config (about:config):
      • browser.tabs.autoGroupNewTabs: true/false (default: true)
      • browser.tabs.autoGroupNewTabs.placement: "after" (default), "first", or "last"
      • browser.tabs.autoGroupNewTabs.delayEnabled: true/false (default: false)
      • browser.tabs.autoGroupNewTabs.delayMs: milliseconds (default: 1000)
      • browser.tabs.autoGroupNewTabs.cancelShortcut: defaults to Alt+ (macOS) / Ctrl+ (Windows/Linux)

New Tab Page

  • Wallpapers: Use curated solid colors, custom colors, or your own image.
  • Optional search bar toggle.
  • Optional weather widget (opt‑in; see Mozilla’s documentation for data usage details).

Migration

  • Firefox Profile Import: Import bookmarks, history, cookies, form history, and passwords directly from a Firefox profile.
    • Note: After importing passwords, restart Waterfox to apply changes.

Web Platform & APIs

  • WebGPU: Enabled, including Web Workers support.
  • Web Share API: Native OS sharing integration.
  • Media: VP8/VP9 hardware‑accelerated decoding for WebRTC video calls.
  • MathML: Updated rendering.
  • Experimental/Behind‑the‑Pref features (availability varies):
    • CSS Masonry layout
    • Prioritized Task Scheduling API
    • DOM: CloseWatcher, H.265 in WebCodecs, Screen Orientation lock, improved Shadow DOM selection, Web Notifications actions
    • CSS: shape() function, font-variant-emoji, @scope rule, scroll‑driven animations
    • SVG: SVG 2 getBBox, improved stroke bounds rendering

Improvements

UI & Customization

  • Menubar styling and tab bar positioning refinements.
  • Default Proton colors aligned with system accent colors.
  • Compact density by default for tighter UI.
  • Status bar restored with hover link readout and widget area.
  • Layout flexibility: move tab bar (top above/below, or bottom) and bookmarks bar (top/bottom).
  • Rich built‑in toggles for tab shapes, spacing, separators, icons, and more.
  • Platform polish:
    • Windows: Mica/backdrop effects where supported.
    • macOS: Titlebar/sidebar blending for a more native feel.
  • Default bookmarks updated with Waterfox‑related links.
  • Smooth scrolling: alternative smooth scroll physics implementation.

Network & Performance

  • POST request efficiency: idempotency‑key headers enabled.
  • Cookies: CHIPS and schemeful SameSite support.
  • Network optimizations:
    • Disabled requests to 0.0.0.0
    • HTTP/3 ECN marking and IP family retry support
    • HTTP retry with half‑open connections
  • Windows: On‑demand loading of keyboard layouts for improved efficiency.
  • Rendering: Dynamic reflow roots enabled.

Privacy & Defaults

  • Reduced promotions: Disabled mobile‑related promos and various third‑party promotional surfaces by default.
  • New Tab Page: Removed search shortcuts from Top Sites.
  • Extension security: Block picker opening from hidden extension pages.
  • Pointer Events: Restricted to secure contexts per spec.
  • macOS: Ctrl‑click no longer defaults to right‑click.
  • Speculative connections: Disabled when typing in the address bar.
  • Remote config: Disabled fetching of remote settings lists; bundled offline copies used instead.
  • A/B testing: Disabled and related code not packaged.

Fixes

  • Private Tabs: No longer retain history.
  • Web Page Translations: Model downloads no longer blocked.
  • Passwords: Autofill works reliably again.
  • Screenshot tool: Restored in the context menu.
  • Duplicate Tabs: Opening a duplicate no longer produces two.
  • Classic extensions: Fixed compatibility so classic style extensions (e.g., TabMixPlus) can be installed again.
  • Theming: Various small polish fixes.
  • Stability: Resolved crashes on certain systems related to optimization flags.

macOS note for beta users

If you used earlier macOS betas, there was a temporary auto‑update issue that required a one‑time manual reinstall and cache removal. The final 6.6.0 build resolves this and normal updates should function going forward.

Underlying platform changes (128.0 → 140.0)

Waterfox 6.6.0 incorporates the upstream platform changes from 128.0 through 140.0. Highlights by version:

129.0 (6 August 2024)

  • HTTPS‑First Mode enabled by default
  • Reader View: character/word spacing, text alignment, contrast themes
  • Offline translation via downloadable language packs
  • Android: Improved page load performance

130.0 (3 September 2024)

  • Partial text translation after full‑page translation
  • Picture‑in‑Picture auto‑open (experimental)
  • Linux: Overscroll animations enabled by default
  • Web Codecs API for desktop platforms

131.0 (1 October 2024)

  • Temporary permissions: Auto‑removal after 1 hour or tab closure
  • Swedish language translation support
  • CHIPS cookie support and enhanced SameSite requirements
  • Linux: Improved HiDPI support with GTK3 font scaling

132.0 (29 October 2024)

  • Wide Color Gamut WebGL (Windows/macOS)
  • macOS: Screen/window sharing selection, automatic session resume
  • Strict tracking protection: All third‑party cookies blocked
  • Post‑quantum key exchange for TLS 1.3
  • Removed: HTTP/2 Push

133.0 (26 November 2024)

  • Bounce Tracking Protection in Strict mode
  • Sidebar access to tabs from other devices
  • Windows: Canvas2D backend changes to platform‑independent backends

134.0 (7 January 2025)

  • Linux: Touchpad gestures with kinetic scrolling interruption
  • Windows: HEVC hardware‑accelerated playback
  • New Tab layout refresh
  • Relaxed popup blocking following HTML specifications

135.0 (4 February 2025)

  • Translation support: Simplified Chinese, Japanese, Korean, Russian
  • Credit card autofill global rollout
  • Certificate transparency enforcement and CRLite checking
  • “Do Not Track” replaced with Global Privacy Control

136.0 (4 March 2025)

  • Sidebar: Quick access to bookmarks, history, synced tabs
  • Vertical tabs: Alternative tab layout option
  • HTTPS‑First for all page loads with HTTP fallback
  • Smartblock: Selective social media content unblocking
  • UK address autofill
  • macOS: Background tab power optimization, HEVC hardware acceleration
  • Linux: AMD GPU hardware video decoding

137.0 (1 April 2025)

  • Tab Groups: Organize tabs with names, colors, save/reopen
  • Address Bar refresh:
    • Unified search buttons
    • Search term persistence
    • Contextual search modes (@bookmarks, @tabs, @history, @actions)
    • Calculator functionality
  • PDF: Automatic link identification and signing
  • Linux: HEVC support

138.0 (29 April 2025)

  • Profile Management: Separate profiles with custom names, avatars, themes
  • Windows 11: Acrylic‑style menus
  • macOS/Linux: Copy links from background tabs

139.0 (27 May 2025)

  • Full‑page translation for extension pages (moz‑extension://)
  • Custom New Tab wallpapers with Celestial category
  • HTTP/3 upload performance improvements
  • PNG transparency preservation when copying
  • Temporal API for date handling
  • Chrome migration: CSV export/import required for passwords/payment methods

140.0 (24 June 2025)

  • Tab unloading capabilities
  • Vertical tabs enhancements
  • Extensions button customization
  • Private browsing security improvements

Packaging and platform status

  • Unity global menu (Linux): Not available in 6.6.0 due to extensive upstream changes; we’re investigating restoration.
  • Linux packaging: AppImage and Flatpak distributions are planned.
  • ARM64 builds: Native builds for Windows and Linux are in progress.

Known issues

  • On Windows, when quitting Waterfox with multiple tabs open, the ‘Close tab’ button in the confirmation modal may appear low-contrast, depending on the selected theme, making it difficult to see.
  • Restart menu command may not execute reliably on Windows.
  • Restart menu item can appear misaligned when menu icons are disabled.

If you’re upgrading from 6.5, you’ll notice both the platform jump and Waterfox‑specific enhancements. As always, if you run into issues, please file them on our issue tracker with details about your OS, hardware, and steps to reproduce.