thunderbird

Greetings once more from the Thunderbird development team!

As the Northern hemisphere summer comes to an end and a slew of PTO, company holidays and projects have wrapped up, what better time to share progress and next steps on the work the Thunderbird Desktop Engineering team has on their plates!?

Exchange support moving well

The powerhouse Exchange engineering team had some great momentum over the summer and completed their work on implementation of the Graph protocol to support email accounts - well in advance of their deadline. They have since moved on to start work to support Exchange calendars using the Graph protocol which is a significant milestone given that our calendar code hasn't had significant changes for some time.

While some team members are now juggling multiple projects, good progress has been made to wrestle the foundations into place, with calendar discovery and persistence in place, along with display of calendar items. Following a brief hiatus to focus on other priorities, the team is once again back into gear.

Keep track of our Graph API Calendar implementation here.

Account Setup & Authentication

Since I last wrote, many of the account setup and account authentication improvements have landed (mostly in versions 156 & 157), unlocking some important security use cases which are becoming more frequently requested and mandated by organizations and legislation around the world.

While diving into the code is an enjoyable adventure, the newly-minted articles devoted to the topic of Oauth customization might be a better starting point for most:
Knowledge Base - Custom OAuth for Thunderbird

UI overhauls - why just one?!

The front end engineering team has completed the rebuild of our account setup manual configuration flows to include new protocol options and security customizations, so it is time to pick up where we left off on our Calendar UI rebuild.

The majority of the front end team is now either focused on Calendar Event data write operations stemming from the Event Read dialog (delete event, RSVPs, Reminders) - or beginning the largest part of the journey, which is the implementation of a new Calendar Create/Edit dialog, along with REDUX-based state management, a new WYSIWYG editor and more reusable components such as date pickers.

Follow the Calendar Event Create/Edit work here

While that work is underway, why not weave in some more improvements?!

After some extensive user research and testing, our design team has begun work to improve the Settings UI, starting with some updates to humanize and homogenize the various options, headings and guidance provided in that area of the application.

Contributions are on the rise! Some AI guidance…

In the past few months, we've seen a wonderful increase in contributions from community members - partially thanks to our move away from Mercurial to a more familiar Git-based workflow - and partially thanks to many LLMs doing a great job of interpreting our public codebase and making it far more accessible. Or it could be that our team is just such a friendly bunch that we've attracted a great group of people willing to support.

Whatever the reason, we're happy to see new names. faces and ideas in our chats and review queue!!

Having said that…We've reached the point where the velocity of work is beginning to pile up and clog our review queue - so I felt it might be time to share some guidance to make the process easier for both external contributors and the internal review team. Bear in mind that while we use AI workflows in several areas, our goal is to preserve a codebase which can be maintained by humans. We're working on a policy that may word some of these points better, but from the past few months of my experience here's what I see as being helpful:

Keep patches to a digestible size and understandable complexity - Contributions should save more development time than it takes to review. If the patch contribution creates heavy work for maintainers, it will be deprioritized - so the best approach is to break the work up into pieces that can be understood more easily and discussed together. Bear in mind that many cloud-based models aren't primarily designed to be frugal with token usage so it's easy for patches to grow (much) larger than they actually need to be to solve the problem. Be specific with prompts to minimize the surface area of changes so they are reviewable.
Humanize or write comments (within code and throughout the code review process) by hand - While we've become accustomed to interacting with a variety of automated systems in our daily lives, a good chunk of the joy involved in our work is to share knowledge with each other and refine the code so that it can be reused and understood by humans.
Be wary of license infringement - much of our work is under the MPL license and we must all take care not to introduce refactored code that originally came from licensed software which can be rewritten and translated using LLM, then relabelled under our licence.
Be transparent - it will often help to share prompts and your model when submitting code for review. Refining all aspects of our workflow is important, and we can all benefit from a collective evolution of skills and prompts that improve over time with input from the team and community.
We encourage contact with a member of the team to discuss approach and architecture in advance of spending time and tokens on a patch. Some areas of the codebase are already slated for redevelopment and it's not always obvious what is underway and planned. Having a quick conversation to say "Hey, I'm thinking about working on this" is a great start to landing something that spends less time in review and uses less tokens, energy & the world's natural resources.
Of course if none of these guidelines are followed, we'll still be very happy to receive help from the wider community - the process may just take longer and be a bit less pleasant.

Enterprise

As parts of the world turn their infrastructure priorities toward digital sovereignty, we've seen an increase in interest from governments, institutions and organizations around the world who are looking to either improve their existing FOSS-based infrastructure or deploy for the first time. That has resulted in some focused efforts throughout Q3 to improve our Enterprise security and policy framework to bring it in line with the strides that the Firefox engineering team has made, and also roll out more Thunderbird-specific administrative mechanisms that allow granular control over end user configurations. Read more about your options and follow the work below:

Thunderbird Enterprise Policies and Relevant Preferences

Thunderbird Enterprise PoC Work Items

Maintenance, Upstream adaptations, Recent Features and Fixes

Waves of changes from upstream Firefox have continually kept the team on their toes throughout July & August, but the small but mighty gang have kept Daily builds largely intact each day. In addition, the team and contributor community have continued landing a series of reliability, stability, and usability improvements across the application. Recent highlights include:

Nico has a series of calendar improvements in the works with several now cleared for landing: D319397, D320418, D320419
Hurtmut has again come to the rescue with a number of patches but most recently solved a widespread filtering problem introduced upstream which will need to be uplifted as a matter of urgency.
Richard pushed many patches since my last update, many related to upstream changes required after the Firefox project "Nova" was unleashed. He's also been on the lookout for other breaking changes such as XUL attribute modifications.
Max was on fire and in constant comms with the team to deliver a large number of important changes but also helped to refine some of our processes relating to AI-driven workflows. Recently, he led an investigation into growing concerns over instability with connections with Gmail accounts in Bug 2028760.
and many more which are listed in release notes for beta.

If you would like to see new features as they land, and help us find some early bugs, you can try running daily and check the pushlog to see what has recently landed. This assistance is immensely helpful for catching problems early.

-

Toby Pilling

Senior Manager, Desktop Engineering

The post Thunderbird Monthly Development Digest: September 2026 appeared first on The Thunderbird Blog.

23 Sep 2026 10:35pm GMT

Bugs resolved in Moz-Phab 2.20.0:

bug 2066178 Drop support for Python 3.9
bug 2068605 preserve file logging from moz-phab list --format json and moz-phab patch --raw
bug 2071586 Review queue reminders should ignore group reviews (at least optionally)
bug 2073088 moz-phab submit is getting the file size from hg/git even if it could infer it from the blob itself
bug 2074036 List index out of range

Discuss these changes in #engineering-workflow on Slack or #Conduit Matrix.

1 post - 1 participant

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23 Sep 2026 4:45pm GMT

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