# Thunderbird: what changed from 154 to 155

- Product: Thunderbird (https://whatsnew.fyi/product/thunderbird)
- Vendor: MZLA Technologies
- Range: changelog entries numbered after 154.0 up to and including 155.0, stable releases only
- Entries below: 1 release (newest first)
- Resolved: 154 is 154.0 and 155 is 155.0, the newest stable release of each major we track
- Carrying security changes: 0 · CVEs mentioned: 0 · Mentioning breaking changes: 0 · Removing or deprecating something: 0
- Page: https://whatsnew.fyi/product/thunderbird/compare/154...155

What's New is an index, not a publisher: every entry below links to the vendor's own release notes, which are the authoritative source. Entries are labelled where they are hand-curated sample data, pre-releases, or drawn from a secondary source such as a developer blog.

Reuse: the summaries, labels and curation here are © What's New. Quote freely with attribution and a link back; wholesale republication of the corpus is not permitted — terms: https://whatsnew.fyi/terms. The vendors' own release notes remain their publishers'.

## What changed (2 changes, grouped by kind)

### Added

#### 155.0 (2026-09-01)

- S/MIME popup shows signature, digest, encryption algorithms and key sizes

### Changed

#### 155.0 (2026-09-01)

- Default address book for manually added contacts is now configurable with mail.addr_book.add_item_default_uri

## Release notes

### 155.0 — Thunderbird 155.0

- Date: 2026-09-01
- Version: 155.0
- Original notes: https://www.thunderbird.net/en-US/thunderbird/155.0/releasenotes/
- Permalink: https://whatsnew.fyi/product/thunderbird/releases/155.0
- Labels: Platforms: Desktop

What’s New S/MIME popup shows signature, digest, encryption algorithms and key sizes Default address book for manually added contacts configurable with mail.addr_book.add_item_default_uri Enterprise p…

- **added** — S/MIME popup shows signature, digest, encryption algorithms and key sizes
- **changed** — Default address book for manually added contacts is now configurable with mail.addr_book.add_item_default_uri