Threads

Fast, readable conversations directly in Thunderbird's message pane.

Select an email or a thread and Threads shows the whole conversation in place: every message as a card, the latest one open, older ones a click away. There is no extra tab, window or sidebar, and nothing leaves your computer.

Requires Thunderbird 147 or newer.

Install

1. Download the latest threads-x.y.z.xpi from Releases.
2. In Thunderbird, open Add-ons and Themes, click the gear menu, and choose Install Add-on From File….
3. Select the downloaded file and accept the permissions.

Threads updates itself when a new release is published. Thunderbird checks for add-on updates about once a day; to check now, use the gear menu → Check for Updates in Add-ons and Themes.

Thunderbird shows a privileged-access notice during installation. Threads replaces the message pane's display using an Experiment API, which add-ons need for that kind of integration. See What Threads can access.

Disable Thunderbird Conversations while using Threads. Both replace the message pane and will conflict.

Using Threads

• Read a conversation. Select any message in a thread. Cards are ordered oldest first by default; long conversations (more than 10 messages) fold the middle messages behind a count you can click to expand.
• Expand and collapse. Click a card's header. While you read a long message, its header stays pinned at the top.
• Quoted text and signatures are tucked away: click ··· to show quoted history, with one bar per reply level. Click the signature line to read the full signature.
• Recipients. Each open card shows a one-line "to … · cc …" summary. Details shows every address. Hover or click an address to filter the folder, create a filter, add a contact, or write to them.
• Attachments appear under the message. Click a name to open it, or use the download button. Save all saves every file to your download folder. Image attachments preview inline.
• More actions. The ⋯ button on each card offers reply, reply all, forward, forward as attachment, mark read/unread, star, open in a new tab or window, show the original message, copy text or Message-ID, save as .eml, archive and move to Trash.
• Original message in the toolbar switches back to Thunderbird's normal message view. The Threads toolbar button switches back.

Settings

Use the sliders button in the reader, or Add-ons and Themes → Threads → Options. Changes apply immediately and are saved in your Thunderbird profile.

• Theme. System, Light, Dark, What Grey, Pitch black, Sepia, Midnight blue, Forest, Plum. With System, a dark desktop uses What Grey.
• Reading. Font (System, Sans serif, Serif, Humanist, Rounded, High legibility, Monospace), text size and line spacing. Only fonts installed on your computer are used.
• Order. Oldest first or newest first.
• Allow remote content. Remote images are blocked unless you turn this on.
• Fold long threads and Show image attachments inline.
• Index controls. Pause or resume the background mailbox index, or rescan after importing old mail.

How it finds conversations

Threads builds a local index of message headers so a conversation can include your replies from Sent and messages in other folders. Indexing starts with the last 30 days, then six months, then older mail. You can read while it runs. Messages are joined only through their References and In-Reply-To headers; matching subjects alone never merge conversations.

What Threads can access

Everything Threads stores stays in your Thunderbird profile. It sends no data anywhere and contains no analytics. Read the full privacy policy.

Permission	Why
Read your email messages, accounts	Show conversations and build the local thread index
Experiment API (full access)	Display conversations inside Thunderbird's existing message pane
Compose	Reply, reply all and forward in Thunderbird's compose window
Update, move and delete messages	Mark read/unread, star, archive and move to Trash from the ⋯ menu
Downloads	Save attachments and .eml files
Address books, mail tabs	Add contacts, filter the current folder by an address
Clipboard (write)	Copy addresses, message text and Message-IDs
Storage	Remember your settings

Limits

• Message text is rebuilt from the original as clean, safe text. Paragraphs, lists, bold, italic, links, code and quotes are kept; HTML layout, colours and custom fonts are not. Use Original message for the sender's exact layout.
• Quote detection follows common mail-client conventions and is not language-aware. Unusual or interleaved replies may land inside the quoted section.
• RSS, news, drafts and templates use Thunderbird's normal view.
• This is an early release. Please report problems with your Thunderbird version and, if possible, the message source (View → Message Source) with personal details removed.

Development

No build step or runtime dependencies: the add-on is plain ES modules. Packaging needs Python 3; tests need Node.js.

npm ci                 # test-only dependency (fake-indexeddb)
npm test
npm run benchmark
python3 build.py       # writes dist/threads-<version>.xpi

Preview the reader in a browser against a mocked Thunderbird API:

python3 -m http.server 8765 --bind 127.0.0.1
# open http://127.0.0.1:8765/tests/preview.html   (?n=40 for a long thread, &slow for slow loads)

How it works internally (indexing, the virtual list, the parser and caches) is in docs/ARCHITECTURE.md.

Releasing

1. Set the new version in manifest.json and package.json, and add a ## <version> section to CHANGELOG.md. Threads uses an Experiment API, so strict_max_version must name the newest Thunderbird it has been tested with; raise it (for example to 159.*) after checking each new Thunderbird release.
2. Run python3 release.py. It builds the XPI, adds it with its SHA-256 hash to updates.json, writes release notes to dist/, and prints the remaining commands.
3. Push the tag, create the GitHub release with the built XPI attached, then push main. Installed copies update once updates.json on main lists the new version.
4. For addons.thunderbird.net, upload dist/threads-<version>-atn.xpi. It is identical except that it leaves out the GitHub update_url, because ATN delivers updates to its own installs.

License

MIT