Thunderbird theme builder

Design a Thunderbird theme, watch it live, download it as a ready-to-install .xpi.

Themes recolour Thunderbird's window chrome — tabs, toolbar, the search field, and the folder pane. They contain no code and request no permissions. The message list and reading pane follow Thunderbird's own light/dark content setting.

Start from

Build from a logo or image

Theme name

Images (optional)

Header background — behind the toolbar/tabs; wide & short. Ships in the .xpi.

Folder-pane background — the left mailbox pane. Ships as a userChrome.css (manual install, see the readme).

Add-on icon — square; shown next to the theme in Add-ons and Themes. Ships in the .xpi.

Folder icons — replace the Inbox/Sent/… glyphs. Ships in the folder-pane .zip (userChrome.css, manual install).

Inbox

Sent

Drafts

Junk

Trash

Archives

Other folders

Live-sync to Thunderbird as I edit

Live preview

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SubjectCorrespondentDate

Re: theme builderClaude9:14

Chrome Web Store reviewBrave8:02

Invoice #1042StripeYesterday

Weekly digestGitHubMon

Re: theme builder

Claude · to you · 9:14 AM

The folder pane picks up the sidebar colours, and the selected folder uses the highlight. Toolbar, tabs, and the search field all follow the theme too.

Ship it.

How to install it (incl. the Ubuntu Snap)

Download the .xpi.
In Thunderbird open about:config, accept the warning, and set xpinstall.signatures.required to false (one time — lets you install your own unsigned theme).
Open Add-ons and Themes → the gear icon → Install Add-on From File… and pick the .xpi.
Snap tip: the file lands in ~/snap/thunderbird/common/Downloads (or your usual Downloads) — browse there in the picker.
No config change? Use about:debugging → This Thunderbird → Load Temporary Add-on → pick the .xpi. It applies until you restart.
To revert: Add-ons and Themes → Themes → enable Default.