Customize Thunderbird 115 Supernova Density, Layout, and Message List

Thunderbird 115 “Supernova” separates several controls that can feel like one setting: density changes the spacing and scale of interface elements, font size changes text, and the View menu changes how the Folder, Message List, and Message panes are arranged. The message list has its own choice between Cards and Table view. Adjusting each control separately makes it easier to get a readable inbox without making the entire window feel oversized.

This practical reference focuses on the menus documented for Thunderbird 115. Mozilla’s current support article for the Appearance panel describes controls for Thunderbird 140 and newer, so those Settings paths may not exist in 115. Menu wording can also differ in later versions. The examples below use only the Supernova-era names.

Quick reference: which setting should you change?

Choose a density that fits the screen

Open the Application Menu (≡) and select Density. Thunderbird 115 offers three choices:

• Compact reduces the space used by interface elements. It can show more folders or messages at once, but small controls and labels may feel crowded.
• Default is a middle-ground starting point if neither spacing extreme feels comfortable.
• Relaxed increases the size and spacing of interface elements. It can make navigation easier on a high-resolution display or when you prefer larger targets, but fewer rows may fit on screen.

Change density, then look at the folder list, message list, and toolbar before making another adjustment. Density controls the general user interface; it is not the same control as text size. If the rows feel appropriately spaced but the labels are hard to read, keep the chosen density and adjust font size instead.

Adjust font size separately

From the Application Menu, choose Font Size, then use the plus or minus control. Increase the size if labels and interface text are too small; decrease it if the interface text takes up too much room. This global adjustment is the first step Mozilla recommends for many font-scaling complaints after an upgrade.

Make one change at a time. For example, if Compact density makes the inbox fit better but the folder names are too small, keep Compact and increase Font Size. If Relaxed density makes icons and controls comfortable but the message subject remains difficult to read, adjust font size rather than repeatedly switching layouts.

Pick a window layout

Use ≡ > View > Layout to choose how the main panes fit together. Thunderbird 115 documents Classic, Wide, and Vertical layouts, with Vertical positioning the Folder pane, Message List pane, and Message pane side by side. The best fit depends on the monitor and whether you spend more time scanning messages or reading them.

• Classic: the Folder pane runs the full window height, with the Message pane immediately below the Message List. Start here if you want a conventional inbox and Table view.
• Wide: the Message pane spans the width of both the Folder pane and Message List pane. Try it when you want more horizontal room for reading a message.
• Vertical: places the Folder pane, Message List pane, and Message pane side by side. It pairs naturally with a wide monitor and Cards view, but the reading pane can become narrow on a small display.

The names are presets for pane arrangement, not separate mail accounts or message modes. You can show or hide individual panes under the same View > Layout menu. For example, press F8 to show or hide the Message pane when you want a taller message list or a larger reading area.

Switch the message list between Cards and Table

The Message List Header contains the current folder name, message count, Quick Filter, and the Message list display options control. If you cannot find the Cards or Table choice, first enable the header under ≡ > View > Layout > Message List Header.

Then select the message list display options control next to Quick Filter and choose:

• Table View when you want a dense list organized into columns such as sender, subject, date, and other fields. It is useful for comparing details across many messages. You can customize which columns appear from the message-list column controls.
• Cards View when you prefer a non-column list with a sender and time on the first line and the subject on the second. In Thunderbird 115, each card uses this two-line presentation. It can be easier to scan at a glance, but it uses horizontal space differently and does not present information as sortable columns.

Cards View is available with Vertical, Classic, or Wide layouts. If the display-options control seems to have disappeared, check the Message List Header setting before changing other preferences; hiding that header also hides the control that switches views.

Reduce folder-pane clutter or bring tags forward

In the Folder pane, open the ⋯ options menu beside + New Message. The menu can show total message counts or folder size, hide the Get Messages and New Message buttons, and hide Local Folders or the Folder Pane Header. The Folder Modes submenu changes which folder groupings appear.

If you use tags as a work queue, enable Folder Modes > Tags to add a Tags section to the Folder pane. Use the small menu beside Tags to move that section up or down. If you rarely use Local Folders, the same pane-options menu can hide them. These are display choices; hiding a pane item does not delete the folders or messages.

Customize the Unified Toolbar

Thunderbird 115 uses a Unified Toolbar across its Spaces, including Mail, Address Book, Calendar, Tasks, Chat, and Settings. Right-click the toolbar (Control-click on macOS) and choose Customize…. Drag available buttons into or out of the toolbar, then finish with Done. The available buttons can include common actions and controls specific to the active Space.

You can also use the keyboard in the customization interface. Mozilla’s toolbar documentation describes Tab and arrow keys for navigation, Enter to add a button, Delete to remove it, and Alt with arrow keys to move items. If you customize the toolbar, keep the commands you use regularly visible and avoid adding so many that the toolbar becomes difficult to scan.

Useful starting combinations

These are starting points, not fixed presets. Narrow windows may make Vertical layout feel cramped; a large display may make Compact density less comfortable. After selecting a combination, open a typical folder and message to confirm that sender, subject, date, folders, and message text remain easy to find.

Troubleshoot text or scaling that still looks wrong

If changing Density and Font Size does not fix unusually large or small interface elements, Mozilla lists several possible causes, including unsupported preferences such as layout.css.devPixelsPerPx or mail.uifontsize, and custom rules in userChrome.css. These are advanced customizations, not normal density controls.

Do not change an advanced preference just to make the inbox more compact. If one of these preferences was changed previously, open ≡ > Settings > General, scroll to the bottom, and select Config Editor…. Search for the exact preference. Mozilla’s Thunderbird 115 FAQ recommends using its reset button if the preference has a changed value. If you use a custom userChrome.css file or an add-on that changes the interface, temporarily disable that customization and reassess the supported Density and Font Size controls before editing advanced settings.

Final check

• Choose Density for spacing and Font Size for text; do not expect one to substitute for the other.
• Select Classic, Wide, or Vertical under View > Layout, then show only the panes you use.
• Use the Message List Header to switch Cards/Table; restore the header if its view menu is missing.
• Use Folder Modes, the folder-pane options menu, and Unified Toolbar customization to reduce clutter.
• Review the resulting inbox at your normal window size before relying on the new layout.

Thunderbird 115’s main window is configurable without editing hidden preferences. Start with the supported Density, Font Size, Layout, and message-list controls, and use advanced resets only when a previous customization has disrupted normal scaling.

Official references

• Thunderbird 115 Supernova FAQ: density, font size, layout, and troubleshooting
• Getting Started with the Thunderbird main window (Supernova and newer)
• Mozilla Support: changing the Classic, Wide, and Vertical layouts
• Mozilla Support: Message List Columns
• Mozilla Support: Unified Toolbar customization
• Appearance panel documentation for Thunderbird 140 and newer
• Thunderbird Blog: Thunderbird 115 Supernova release overview
• Thunderbird Blog: font scaling and density troubleshooting