v3.4.10

• Fixed an issue where the Findbar displayed the wrong background color.

v3.4.9

• Fixed a regression introduced in v3.4.8 where the address bar outline no longer appeared on hover.
• The search box on the New Tab page now also supports the uc.flex.revert-to-original-flat-corner-style option, allowing it to revert to Firefox's default rounded corners.

v3.4.8

• Fixed misalignment between the address bar and its suggestion dropdown when the URL bar is focused.

• Added a new option uc.flex.revert-to-original-flat-corner-style. When set to true, this restores Firefox's default flatter corner style instead of FlexFox's rounded design. You can also customize the corner radius of the address bar, search bar, and find bar by adjusting the *-radius variables under this option in uc-variables.css.

  

v3.4.7

• Fixed an issue where the native vertical tabs couldn't smoothly expand when placed on the right and the mouse moved to the edge of the screen.
• Fixed missing scrollbars when native vertical tabs were on the right side.
• Adjusted spacing to ensure proper left padding when vertical tabs expand from the left.

v3.4.6

• Fixed layout issues with tab group labels in Firefox v140+, where size and alignment were incorrect.
• Restored the separator between pinned and regular tabs when using uc.flex.show-pin-tabs-separator-in-expanded-state in Firefox v140+, which had stopped appearing due to structural changes.

v3.4.5

• Fixed a regression introduced in v3.4.3 where the width of the native vertical tabs in collapsed mode was incorrect.

v3.4.4

• Fixed an issue that prevented Sidebery from expanding in Nightly v140.

• Improved theme compatibility: if the theme includes a background image (even a transparent one), FlexFox now automatically allows the theme to override the built-in color palette, without needing to manually enable uc.flex.allow-addons-to-change-toolbar-color.

• Added support for Firefox Color, allowing users to freely customize the browser's appearance.

  • To allow Firefox Color themes to override FlexFox's built-in palette, select any background image in the Custom backgrounds tab on the Firefox Color site.
  • Some Preset themes in Firefox Color do not include background images. To make them apply fully, either pick a background image or manually enable the uc.flex.allow-addons-to-change-toolbar-color setting. Without a background image or this setting, text colors may change, but toolbar backgrounds will not.

Here's how FlexFox looks with the Rosé Pine Moon theme applied via Firefox Color:

v3.4.3

• Fixed an issue where enabling uc.flex.add-ui-text-stroke caused Sidebery to use an unintended font.

• Fixed extra padding after the first navigation bar item when using horizontal tabs.

• Improved compatibility when only the new sidebar is enabled without native vertical tabs:

  • Sidebar stripe now highlights correctly.
  • Sidebar settings button no longer shifts position when the stripe expands.

[!NOTE] Using the new sidebar without native vertical tabs is still not recommended, as FlexFox is designed and optimized around the vertical tab layout.

v3.4.2

• Fixed layout issues with native vertical tabs in Firefox v138 when using Always-Open Mode. Incorrect width handling caused jitter on hover and misalignment of the bookmarks toolbar.

v3.4.1

• Fixed an issue where the sidebar stripe did not expand to the correct height when Sidebery was fully hidden.
• Fixed incorrect width when expanding the native vertical tabs while the sidebar was on the right and fully hidden.
• Fixed an issue where native vertical tabs could not be expanded when both uc.flex.disable-native-vertical-tabs-autohide and uc.flex.fully-hide-sidebery were enabled.
• Deprecated uc.flex.disable-native-vertical-tabs-autohide. Use uc.flex.disable-sidebery-autohide instead to enable always-open mode for both Sidebery and native vertical tabs.

v3.4.0

• Fixed an issue where the trigger area for showing Sidebery after hiding it via shortcut could not use the custom width set by --uc-hover-sidebar-trigger-width.
• Major update: FlexFox now supports fully hiding the built-in vertical tabs. The existing option uc.flex.fully-hide-sidebery and the shortcut Hide Sidebery now also apply to native vertical tabs. When entering fullscreen mode (F11), native vertical tabs are automatically hidden as well. When the window is not maximized, the --uc-hover-sidebar-trigger-width value also controls the trigger area for native vertical tabs. This means all settings that apply to Sidebery—such as show/hide speed—now apply to native vertical tabs too, offering a unified behavior.

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v3.3.5

• Fixed extra spacing around menu icons introduced in Firefox v140+.

v3.3.4

• When the sidebar button is not at the first or last position on the navigation bar, its size will now revert to the standard toolbar icon size instead of being enlarged.
• The List all tabs button icon has been updated for better visual harmony with the colored bookmark folders. You can revert to the original Firefox icon by setting uc.flex.revert-to-original-sidebar-icon to true.

v3.3.3

• Fixed an issue where corner rounding was not rendered correctly in native vertical tabs mode.

v3.3.2

• The header stripe in native horizontal tab mode now supports gradient highlights. (By the way, you can customize the gradient color using the --uc-gradient-highlight variable.)
• Fixed an issue where the sidebar button overlapped with the window controls when placed at the far right in horizontal tab mode.
• Left padding is now always added when bookmarks items are the second element in the navigation bar, unless uc.flex.disable-nav-bar-first-item-right-padding is explicitly set to false.
• When Sidebery is inactive, native Firefox rounded corners for vertical tabs and the content area are restored. To revert to square corners, set the built-in Firefox option sidebar.revamp.round-content-area to false.
• Fixed an issue where a menu icon displayed the wrong image.

v3.3.1

• Add shortcut for hiding all topbars and Sidebery.

v3.3.0

• Fixed an issue where Sidebery would not expand when using expand-on-hover together with uc.flex.fully-hide-sidebery or in fullscreen mode.
• Resolved a display issue where the sidebar toggle button appeared misaligned when positioned on the far right of the screen.

v3.2.8

• Removed the uc.flex.add-bookmarks-left-margin option. Padding is now automatically added after the first item in the navigation bar when using native vertical tabs or Sidebery. This visually separates it from the rest of the toolbar items and aligns it more cleanly with the vertical tab column. The spacing adjusts dynamically and disables itself in fullscreen or when vertical tabs are hidden.
• Added a new option: uc.flex.disable-nav-bar-first-item-right-padding, which disables the above behavior.
• The sidebar toggle icon is now replaced with the FlexFox logo. Although it's designed to appear on the far left of the navigation bar, users can move it freely using Firefox's Customize Toolbar. If the sidebar is placed on the right, Firefox normally moves this icon to the far right of the navigation bar, but FlexFox pushes it even further to the edge of the screen—past the hamburger menu and window controls—so it aligns cleanly with the right-side vertical tabs.
• Added option: uc.flex.revert-to-original-sidebar-icon, which restores Firefox's default sidebar icon.
• Added option: uc.flex.revert-to-original-bookmark-star-icon, which brings back Firefox's original bookmark star icon (instead of FlexFox's heart-shaped version).
• Experimental feature: uc.flex.enable-gradient-highlight adds gradient colors to the FlexFox logo, the sidebar stripe, and the bookmark star icon. The value should be set to 0 (off) or 1 (on). Only one preset gradient is currently available, but support for more areas and styles is planned for future updates.

v3.2.7

• Added uc.flex.disable-menu-icons option to allow disabling menu icons.

v3.2.6

• Fixed the size of an icon.

v3.2.5

• Added missing icons for some menus.

v3.2.4

• When the sidebar setting “Expand sidebar on hover” is enabled, FlexFox now defers to Firefox's native auto-collapse behavior for vertical tabs. In this mode, Sidebery also supports toggling between auto-collapse and keep expanded states using the Ctrl+Alt+Z shortcut or the sidebar toggle button.
• A new preference, uc.flex.disable-sidebery-hover-animations, has been added to disable hover animations in Sidebery when it is pinned open. This helps reduce slight visual jitter caused by those animations, though it may slightly impact the visual neatness of the collapsed state.

v3.2.3

• Continued fixes for display glitches in expand-on-hover mode (native vertical tabs).

v3.2.2

• Fixed various display issues when using Firefox's native vertical tabs in expand-on-hover mode.

v3.2.1

• Fixed an issue where native vertical tabs were obscured by the sidebar when expanded.

v3.2.0

• Fixed a bug where the sidebar toggle button lost its background on hover.
• Full support for Firefox v138's native vertical tabs in expand-on-hover mode.
  When the new sidebar setting “Expand sidebar on hover” is enabled, FlexFox's own auto-collapse feature for vertical tabs is disabled in favor of the native behavior.
  In this mode, the width of the vertical tab bar can be freely adjusted.

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v3.1.9

• Fixed an issue where the sidebar toggle button would disappear when a theme was applied.
• Fixed incorrect layout offsets for the bookmarks toolbar and navigation bar when Sidebery's auto-hide was disabled.

v3.1.8

• Removed the sidebar header that now appears in web extension panel windows (introduced in Nightly v140), restoring the intended compact layout for extensions like Sidebery.
• Adjusted alignment between the navigation bar and vertical tabs.

v3.1.7

• Fixed a timing issue in the native vertical tabs animation. Tab label appearance now syncs properly with the tab width expansion.
• Improved the file size estimation in the PowerShell installer script to more accurately reflect the actual download size.

v3.1.6

• Users can now create a uc-custom-content.css file in the content folder to apply custom styles for web content. It is imported at the end of userContent.css, allowing it to override previous styles. Since this file is not part of the FlexFox repository, its contents will remain untouched during future updates.
• Restructured the project directory to simplify the update process for users who update via Git clone and pull. This change also lays the foundation for the upcoming install/update script.

v3.1.5

• Reduced unnecessary style rules when the new sidebar is enabled.
• Fixed a long-standing bug in the classic sidebar where the sidebar would collapse when hovering over the switcher menu.
  Note: This bug had existed for quite some time. Since its impact was minor and fixing it required a slight performance cost, it was previously left unaddressed. Now that FlexFox has fully transitioned to the new sidebar, this patch closes the chapter on the legacy version with a proper fix.

v3.1.4

• Fine-tuned the positioning of the findbar.

v3.1.3

• Fixed an issue where the findbar failed to display match count when positioned in the bottom-right corner.

v3.1.2

• The default position of the findbar has been changed from top-center-left to top-right. A new string-based preference uc.flex.findbar-position has been added:
  • "top-center-left" or "0" moves the findbar to the previous default location near the top center-left.
  • "top-right" or "1" places it in the new default location at the top right.
  • "bottom-right" or "2" sets it to Firefox's original position at the bottom right.
• The --uc-findbar-top variable has been removed. Findbar placement is now controlled using --uc-findbar-x-position and --uc-findbar-y-position, allowing full customization.
• The hardcoded minimum width of the sidebar has been removed. The value is now fully controlled via the --uc-sidebar-width variable.

v3.1.1

• Updated the default animation for collapsing/expanding Sidebery to ease-in-out to match Firefox's native vertical tabs (previously Sidebery used linear). Users can customize the transition type via the --uc-autohide-transition-type variable in uc-user-settings.css.
• The animation type for Firefox's native vertical tabs is now also controlled by --uc-autohide-transition-type, allowing user customization.
• Fixed an issue where enabling the uc.flex.fully-hide-sidebery option in a non-maximized window would leave unwanted blank space at the edge and cause incorrect Sidebery height.

With this update, all previously missing features from the horizontal tab mode are now fully compatible with Firefox's native vertical tabs. FlexFox v3.1.1 brings complete feature parity, making it seamless for users to switch from the old setup.

v3.1.0

• Refactored the structure of uc-variables.css. Frequently used and user-customizable variables are now grouped at the top of the file with clearer descriptions.
• Overhauled the logic for overriding the toolbar background color in FlexFox. This update should fully resolve issues with theme background image alignment, transparency handling, and incorrect display when the window is inactive.
• Improved animation smoothness when expanding or collapsing vertical tabs.
• Adjusted the navbar positioning so that its buttons align better with vertical tabs.
• Toggling uc.flex.allow-addons-to-change-toolbar-color no longer causes the sidebar to shift vertically.

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v3.0.7

• Fixed incorrect background highlight for the active tab when using Firefox's native tabs (both horizontal and vertical layouts).
• Fixed a visual glitch in themes where the background image did not align properly between the navigation bar and bookmarks bar, when the menubar was shown and the bookmarks bar was set to auto-hide.
• Fixed an issue where the menubar background color did not update correctly when the Firefox window was inactive.

3.0.6

• Updated multiple imported styles to their latest versions.
  • Added a closing animation to the find bar when it loses focus.
  • Improved behavior to keep the navigation bar visible when various panels are open.
• Fixed a non-standard syntax to prevent potential bugs and ease future debugging.

v3.0.5

• Fixed the position offset of the sidebar stripe when uc.flex.allow-addons-to-change-toolbar-color is enabled.

v3.0.4

• Fixed a typing mistake.
• Fixed the horizontal offset of the bookmarks toolbar when the new sidebar option Hide tabs and sidebar is enabled.

v3.0.3

• Fixed an issue where the sidebar stripe could not expand when uc.flex.fully-hide-sidebery was enabled or in fullscreen mode. This update also resolves a transition desync between the sidebar stripe and Sidebery under the same conditions.
• Corrected a theme color issue where the menu bar displayed an inconsistent background color compared to the navigation toolbar.

v3.0.2

• Fixed animation issue when the new sidebar is placed on the right side.
• Native vertical tabs now use the same expand/collapse speed as Sidebery. You can adjust the speed using the uc.flex.sidebery-fast-hover-expand or uc.flex.sidebery-slow-hover-expand options, or by directly modifying the --uc-autohide-* and --uc-hover-* variables to suit your preference.

v3.0.1

• Fixed an issue where the position of the sidebar stripe was incorrect when both uc.flex.disable-bookmarks-autohide and the new sidebar were enabled.
• Fixed an issue where the width of the sidebar stripe displayed incorrectly when both uc.flex.disable-sidebery-autohide and the new sidebar were enabled.

v3.0.0

• Integrated Firefox's native vertical tabs with Sidebery.
  • When Sidebery is active, the native vertical tabs are automatically hidden. The new sidebar collapses into a slim colored stripe at the top of Sidebery. Hovering over the stripe reveals the sidebar toolbar buttons.
  • When Sidebery is inactive (e.g., when another sidebar tool or extension is opened), the native vertical tabs are shown instead.
  • When using the F1 key to quickly toggle Sidebery, since Sidebery and native vertical tabs share the same width and layout, the switch appears seamless.
  • Supports automatic layout adjustment for both left- and right-sided sidebars, adapting to different UI placements.
• Added a new numeric option uc.flex.max-visible-vertical-pinned-tabs (accepted values: 4–6). This controls how many pinned tabs can be displayed vertically in each column of the native vertical tabs panel. The default is 4. If the number of vertically stacked pinned tabs exceeds this, a scrollbar will appear.

[!IMPORTANT] Built-in vertical tabs now automatically collapse and expand on hover. Use the Expand sidebar button (Alt+Ctrl+Z) to enable this feature.

🖼️ Auto-collapse demo for native vertical tabs

Native vertical tabs expanded, with uc.flex.show-pin-tabs-separator-in-expanded-state set to false

Native vertical tabs collapsed, with uc.flex.show-pin-tabs-separator-in-expanded-state set to false

[!TIP] Users can now create a uc-user-settings.css file in the components folder to customize FlexFox styles. This file loads after FlexFox and overrides its styles, so custom changes remain intact even after future updates.
See this section: User-Customizable Styles (uc-user-settings.css)

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v2.1.2

• Fixed an issue where the bookmarks bar would shift when both native vertical tabs and uc.flex.disable-bookmarks-autohide were enabled.
• Fixed a delay in the URL bar transition when entering fullscreen mode.

v2.1.1

• Fixed an issue where the native vertical tabs background became transparent in Firefox v137.
• Added the uc.flex.disable-native-vertical-tabs-autohide option to disable auto-collapsing of native vertical tabs when set to true.

v2.1.0

• Built-in vertical tabs now automatically collapse and expand on hover. Use the Expand sidebar button (Alt+Ctrl+Z) to enable this feature.
• Added a new option uc.flex.show-pin-tabs-separator-in-expanded-state to display a separator line in the pinned tabs panel when using native vertical tabs.
• Fixed an issue where themes couldn't be applied when using built-in vertical tabs, and a bug where the theme background image broke when auto-hiding the bookmarks bar.
• Users can now create a uc-user-settings.css file in the components folder to customize FlexFox styles. This file loads after FlexFox and overrides its styles, so custom changes remain intact even after future updates.
• Native vertical tabs and Sidebery are not yet integrated. Only one can be used at a time.

The sidebar tool button design is based on firefox-gx by @Godiesc. Thanks to @Godiesc for the excellent implementation.

v2.0.3

• Added sidebar-positionend attribute for compatibility with Firefox v138+, with a slight tweak to the width of the new sidebar.

v2.0.2

• Updated @media rule for Firefox v137+ compatibility.

v2.0.1

• Added a 1px border to the top when the window is not maximized.
• Cleaned up the styles by removing unnecessary rules and comments.

v2.0.0:

• Completely rewritten core functionality, achieving a 28x speed improvement over the previous version.
  • The first right-click menu opening after launch now takes just 13ms, matching Firefox's native theme performance.
  • Opening the "List All Tabs" menu with 205 tabs takes 26ms, also on par with the native theme.
  • In other words, after this rewrite, v2.0.0 has almost no impact on Firefox's performance.
• Fixed display issues with the address bar and native vertical tabs in Nightly (v135).

🖼️ Experience the new feature in action

FlexFox with the dark theme and uc.flex.disable-sidebery-autohide enabled:

Combined with uc.flex.fully-hide-toolbox:

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v1.1.1:

• Resolved an issue where the Findbar's background color did not display correctly when a theme was applied.

v1.1.0:

• Fixed background image clipping on hover with bookmarks toolbar auto-hide enabled and theme background active.
• Adjusted zoom level text brightness.
• Corrected window controls positioning in Nightly (v135). Resolved compatibility with customtitlebar after tabsintitlebar deprecation.
• Added preference uc.flex.disable-sidebery-autohide to disable Sidebery auto-collapse.

[!IMPORTANT] Before importing the v1.1.0 version of sidebery-styles.json, clear the old styles first. Open Sidebery settings (via the gear icon) > Styles editor > clear all styles under both the Sidebar and Group page sections, then import the new styles.
Importing sidebery-settings.json may occasionally cause panel data loss. Be sure to create a snapshot backup of your panel data beforehand.

v1.0.4:

• The zoom level icon is now always visible when the webpage is not at the default zoom level.
• The bookmark star icon is now always visible when the webpage has already been bookmarked.
  
  

v1.0.3:

• Optimized performance when the uc.flex.allow-addons-to-change-toolbar-color option is enabled, improving speed by 1.4x compared to v1.0.2.

v1.0.2:

• Improve URL bar switcher and chicklet visuals.
• Add option uc.flex.allow-addons-to-change-toolbar-color to allow themes and addons to customize toolbar background image and color.
  

v1.0.1:

• Fixed the issue where the tracking protection icon in the URL bar was not hidden.
• Added uc-pdf.js.css.
• Added LICENSE file.

v1.0.0:

• Performance has improved dramatically, running 100x faster than previous versions. Opening the context menu now only adds 16ms of latency compared to the default interface.

[!IMPORTANT] If you previously used FlexFox on Firefox versions earlier than v133, reset all settings by navigating to about:config, searching for uc.flex., and removing all entries before updating.

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