fidzu : thunderbird

Welcome to the Q2 edition of the Engineering Effectiveness Newsletter! The Engineering Effectiveness org makes it easy to develop, test and release Mozilla software at scale. See below for some highlights, then read on for more detailed info!

Highlights

• Improved mach startup overhead by 30-50%, as well as a 75% improvement for mach test on Windows and 10s faster configure for subsequent runs

• Moved to weekly scheduled dot releases and faster rollouts, allowing us to deliver fixes and uplifts to users faster and more reliably

• Created a huge number of dashboards to help developers dig into Mochitest and XPCShell tests

• Stood up MacOS worker pools that can run multiple tasks at once using VMs, greatly improving our Mac capacity issues

• Can now navigate to about:pdf in Nightly to open and edit arbitrary PDF files, including the ability to set Firefox as your default PDF editor on MacOS

Detailed Project Updates

AI for Development

• Suhaib Mujahid deployed the initial version of Hackbot, a platform for building and running AI agents to automate parts of the Firefox development workflow.

• Evgeny Pavlov ported the "Build Repair Agent" to Hackbot and deployed it for testing. It now monitors Firefox build failures and triggers the agent. When an analysis and a proposed patch are ready developers can be notified by email.

Bugzilla

• David Lawrence added a new GitHubPullRequests extension that renders a live status panel in the bug modal for any attachment whose content type is text/x-github-pull-request. A new REST endpoint fetches PR metadata (state, author, labels, latest review per reviewer) from the GitHub REST API on demand, and a client-side script populates a table with a "show closed/merged" toggle.[image]

• Xavier L'Hour improved the user experience for developers, adding shortcuts to buglist.cgi for all, open, or closed bugs (1764713)

• Xavier L'Hour added a new shortcut button to the bug page that allows users to quickly move spam bugs to the Invalid Bugs product (1684509).

Build System and Mach Environment

• Alex Hochheiden has been moving build system logic out of make to pave the way for a new build system backend (coming soon). See Bug 2038789.

• Alex Hochheiden landed a 30%-50% (platform dependent) speedup for mach startup. See Bug 1775197.

• Alex Hochheiden sped up subsequent configure runs by ~10s by adding caching to the mach taskgraph toolchain step. See Bug 2017746.

• Alex Hochheiden reduced mach test startup overhead on Windows by 75%. See Bug 2018327.

• Alex Hochheiden has achieved significant code deduplication and simplification by consolidating the Android Gradle configuration into convention plugins. There were also various Gradle configure-cache improvements. See Bug 2007013, Bug 1950099, Bug 2013417, Bug 2017752, and Bug 2017753.

Firefox-CI

• Julien Cristau added support for interactive tasks (aka one click loaners) on Windows and macOS

• Andrew Halberstadt implemented mach try support with Github, being used in mozilla/enterprise-firefox-try and coming to Firefox soon.

• Andrew Halberstadt implemented the machinery to start making Gecko CI tasks clone from Github.

• Ryan Curran brought Firefox CI's Apple Silicon VM infrastructure into production. Building on the MacOS CI image pipeline established last year, he migrated test suites onto virtual machines and grew the macosx1500-aarch64-vms pool so Taskcluster now routes eligible jobs to VMs alongside physical hardware. This reduces reliance on physical Macs, increases CI capacity, and supports the ongoing migration off of older Intel-based macOS infrastructure

• Jonathan Moss migrated Firefox CI's cloud-based Windows testing from Windows 11 24H2 to 25H2, moving the bulk of Firefox's Windows test coverage to Microsoft's latest platform and keeping CI aligned with the Windows version most commonly used by Firefox Desktop users

• Florian Quèze created many dashboards to help dig into Mochitests and XPCShell tests

• Ryan VanderMeulen landed a set of improvements to mach try chooser. The update adds an exclude filter, a clearer preview pane with removable job rows, an artifact-builds toggle, and a warning when a selection exceeds task-prioritization thresholds. It also fixes a bug where choosing Firefox for Android jobs would unintentionally clear selections for other platforms.

Lint, Static Analysis and Code Coverage

• Valentin Rigal and Bastien Abadie created a Code Review Bot prototype for publication of review comments using various source linters on Github

• Morgan Rae Reschenberg added support for accessibility review to Code Review Bot

Mozregression

• Zeid fixed a bug in mozregression-gui on macOS, where the camera and microphone capture request was getting rejected (released in 7.3.0). Thanks to bug report + tip from Andreas Pehrson.

PDF.js

• Calixte added about:pdf to use an entrypoint for opening and editing arbitrary PDF files[image]

• Calixte added support for playing videos/sounds embedded in PDF files

Phabricator , moz-phab, and Lando

• Connor Sheehan improved the uplift experience by leveraging Lando to manage the assessment forms, train selection, and automatic application, so conflicts are detected earlier. The number of uplifts via Lando has out-paced those via Moz-Phab, and sailed through the rise in uplift numbers (likely due to more sec-bugs getting fixed and uplifted).

• Zeid added support for private GitHub repositories in Lando, allowing security patches to be implemented in a private clone of a repo, and pushed to the public one.

• Olivier Mehani finalized support for using the new Lando instance for try-pushes. This brings a host of QoL improvements which weren't backported to the old instance: better UTF-8 support, smarter conflict resolution and improved security and authentication. It is now processing about 1500 pushes / week (old Lando still processes about 50 / week).

• Magnolia Liu implemented automatic pushes to Try for uplift requests, for faster feedback in case of issues.

• Olivier Mehani added a view of a user's current and recent jobs on the landing page of Lando when authenticated.

• Zeid identified and fixed the causes of some stability and reliability issues in Lando, which were causing increased downtime during deployments and on an ongoing basis.

• Olivier Mehani deployed a PoC of reviewer selection on the GitHub pilot, allowing Herald-like mechanisms to GitHub PRs.

• Olivier Mehani and Connor Sheehan (with Corey Bryant and Daniel Darnell) migrated the COMM project to GitHub https://github.com/thunderbird/thunderbird-desktop, sharing Firefox's syncing model.

Release Management and Engineering

• Donal Meehan drove the Release Management team's move to a weekly scheduled dot release cadence for Desktop and Android, starting with Firefox 151. This allows us to deliver fixes and approved uplifts to users faster and more predictably. This change is expected to reduce unplanned releases, improve release flexibility, and create a more consistent release rhythm across teams.

• Dianna Smith drove the update to the Release Management team's Desktop major release rollout process, starting with Firefox 152. Instead of throttling to 0% on day 2, it will remain at 25% rollout for two days before moving to 100%, unless any issues arise. This should help us collect uptake and stability signals earlier while still allowing time to catch problems before full rollout.

• Pascal Chevrel completed the update to the dictionaries shipped with Firefox Desktop. The update added eleven new dictionaries, covering Croatian, English (UK), Georgian, Persian, Slovenian, Tajik, Tamil, Tibetan, Turkish, Welsh, and Xhosa, and refreshed nine others. This expanded the number of locales with a built-in spellchecker from 30 to 41 beginning in Firefox 152. Special thanks to Francesco Lodolo, Bryan Olsson, and the localization community for reviewing the patches and helping assess the quality of the dictionaries.

• Pascal Chevrel delivered a range of improvements to WhatTrainIsItNow, including expanded it to cover weekly dot releases and ESR planned dot releases, added new uplift views including a dot-release uplifts page and a beta uplift graph, and published new APIs that surface train-selection and uplift guidance inside Lando. He also made performance improvements and a steady stream of fixes across the site.

• At Pwn2Own 2026, Firefox came through with no successful exploits, thanks to preparation across many teams and individuals. Within Release Management, Ryan VanderMeulen drove pre-event patch readiness and Dianna Smith coordinated the releases during the event, including the 150.0.3 dot release, which mitigated the root cause behind several of the contest entries.

• Dianna Smith built out release-health monitoring and alerting in Bigeye, giving Release Management a growing set of automated alerts that surface data anomalies earlier to aid in release health and regression detection. To make the capability easy to extend, she also created a guide for other teams to add monitoring and alerts for the areas they know best. Teams that want an earlier signal on their own metrics are encouraged to use the guide and help grow the coverage.

Release Operations

• Ryan Curran built Hangar, a live dashboard for monitoring Firefox CI's worker pools. It consolidates fleet data from several systems into one view, giving Release Operations a single place to check fleet health and catch problems such as missing or quarantined workers early.

• Ryan Curran created the iOS version of BuildWatch, and Andrew Erickson ported it to Android. BuildWatch lets you monitor Firefox CI try pushes from your phone, including live per-platform build status, failure summaries, and one-tap retriggers. It uses only public APIs, so no VPN is required.

• Andrew Erickson and Mark Cornmesser developed Fleetbench, a tool for benchmarking Firefox CI workers. It currently measures CPU and ADB/USB I/O performance, helping Release Operations identify slow or outlier hosts before they skew performance test results such as Speedometer and trigger noisy or false regressions.

• Andrew Erickson built Pool Classifier, a web app for viewing per-worker success rates across Taskcluster worker pools. It classifies newly completed tasks every 15 minutes, giving Release Operations a continuously updated view of worker health and helping surface problematic workers proactively.

• Andrew Erickson created Fleetroll, a command-line tool Release Operations uses to manage and monitor long-running Linux, macOS, and Windows hardware hosts in Firefox CI Taskcluster. It deploys Puppet branch overrides and Vault secrets, audits what is actually applied, and surfaces each host's Puppet and Taskcluster state in a live dashboard.

• Mark Cornmesser built out a set of new worker-metrics dashboards in Yardstick, giving Release Operations clearer real-time visibility into the health of the Firefox CI hardware fleet. These include Linux worker status, Windows worker CPU and disk metrics, and a Windows job pickup and wait timeline, with alerting on key thresholds. The full set lives in the FXCI Hardware Workers folder in Yardstick.

• Jonathan Moss expanded cloud cost reporting in Looker, adding Azure support alongside the existing GCP data and a cloud-provider filter on the FXCI task overview dashboard. The team can now break down Firefox CI compute costs by cloud provider, making it easier to track and compare spend across Azure and GCP.

Taskcluster

• Yaraslau Kurmyza added Azure fast deprovision taskcluster#8790 and concurrency taskcluster#8815 to improve worker scanner performance. This shows ~2x-4x scan time improvements already.

• Contributor nitishagar and Yaraslau Kurmyza added patches taskcluster#8514, taskcluster#8784 to support compression in Taskcluster services API and Yarik worked with Fastly to resolve broken brotli support on the WAF edge side. Now services transmit significantly less data.

• Yarik added a dedicated service account to log with read only permissions webservices-infra#11197. This allows tc-logview to be used safely by untrusted agents inside containers with narrow short-lived access tokens.

• Yarik published queue forecasting dashboard experiments that continuously collects task events and trains models to enable and improve predictions on a task level (how long will it run, and when will it start). With future plans including extending it to the whole task group (mach try)

Treeherder

• Florian Quèze added treeherder#9540 "Show task group profile" item to the push action menu

• Cameron Dawson, juungo and moijes12 implemented various Treeherder API performance improvements

• Heitor Neiva added Git branch labels to pushes in Treeherder

• Andrew Halberstadt implemented the ability for Treeherder to display multiple Git branches at once, enabling support for "try like" repositories in Github

Version Control

• Upgrade hg.mozilla.org to Mercurial 7.2.2

• Created the mozilla-esr153 and comm-esr153 repositories.

Other

• Sylvestre converted our documentation from reStructuredText to MyST flavored Markdown

Thanks for reading and see you next quarter!

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09 Jul 2026 4:26pm GMT

The latest version of the Firefox Profiler is now live! Check out the full changelog below to see what's changed:

Highlights:

• [Florian Quèze] Add "/" and "f" keyboard shortcuts to focus the panel filter box (#6025)
• [Markus Stange] Change profile.shared.stackTable.prefix to prefixOffset (delta from current index) (#6089)
• [Markus Stange] Implement column sorting in the marker table (#6083)
• [cathaysia] feat: invert call stack in flame graph to render as icicle graph (#6090)

Other Changes:

• [Sky Ning] Add workflow to insert PR preview links (#6133)
• [Markus Stange] Make it easier to create upside-down flame graphs (#6128)
• [Markus Stange] Use appropriate highlighter dialects for ts + jsx (#6141)
• [cathaysia] style: add .editorconfig (#6142)
• [Nazım Can Altınova] Prevent long source URLs from overflowing the code error overlay (#6147)
• [Nazım Can Altınova] Extract a runCommand helper for profiler-cli command handlers (#6148)
• [cathaysia] feat(theme): add color-scheme meta (#6150)
• [Nazım Can Altınova] Add an early throw for the this.querier and remove the non-null asserts in the cli codebase (#6145)
• [skylarkning] Improve preview link discovery (#6149)
• [Nazım Can Altınova] Sync: l10n → main (July 9, 2026) (#6155)

Big thanks to our amazing localizers for making this release possible:

• de: Michael Köhler
• el: Jim Spentzos
• en-GB: Ian Neal
• es-CL: ravmn
• fr: Théo Chevalier
• fy-NL: Fjoerfoks
• ia: Melo46
• it: Francesco Lodolo [:flod]
• nl: Fjoerfoks
• ru: Valery Ledovskoy
• tr: Nazım Can Altınova
• zh-TW: Pin-guang Chen

Find out more about the Firefox Profiler on profiler.firefox.com! If you have any questions, join the discussion on our Matrix channel!

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09 Jul 2026 1:58pm GMT

The Rust team is happy to announce a new version of Rust, 1.97.0. Rust is a programming language empowering everyone to build reliable and efficient software.

If you have a previous version of Rust installed via rustup, you can get 1.97.0 with:

$ rustup update stable

If you don't have it already, you can get rustup from the appropriate page on our website, and check out the detailed release notes for 1.97.0.

If you'd like to help us out by testing future releases, you might consider updating locally to use the beta channel (rustup default beta) or the nightly channel (rustup default nightly). Please report any bugs you might come across!

What's in 1.97.0 stable

Symbol mangling v0 enabled by default

When Rust is compiled into object files and binaries, each item (functions, statics, etc) must have a globally unique "symbol" identifying it. To avoid conflicts when linking together different Rust programs, Rust mangles the original name of items to include additional context such as the module path, defining crate, generics, and more. Historically, this mangling was based on the Itanium ABI, also (sometimes) used by C++.

The new mangling scheme resolves a number of drawbacks from the previous one:

• Generic parameter instantiations preserve their values, rather than being tracked solely behind a hash
• Inconsistencies: not all parts used the Itanium ABI, meaning that custom demangling was still necessary

Since Rust 1.59, the compiler has supported opting into a Rust-specific mangling scheme via -Csymbol-mangling-version=v0. Since November 2025, this scheme has been enabled by default on nightly, and 1.97 is now enabling it on stable Rust. The legacy mangling scheme can only be enabled on nightly, and the current plan is to fully remove it.

See the previous blog post for more details.

Cargo support for denying warnings

It's common practice to deny warnings in CI. Historically, doing so is typically done through RUSTFLAGS=-Dwarnings. With Rust 1.97, Cargo controls how warnings interact with build success: either silencing them (via allow level), rendering without failing (default, warn), or denying them (via deny).

As a result of Cargo configuration determining the behavior, using this feature doesn't invalidate the underlying build cache, meaning that it's easy to temporarily opt-in. For example, if warnings are adding unwanted noise while working through fixing errors after a refactor, you can run CARGO_BUILD_WARNINGS=allow cargo check, temporarily silencing them.

In CI, jobs can instead set CARGO_BUILD_WARNINGS=deny to deny warnings. This can be combined with --keep-going to collect all errors and warnings rather than stopping on the first failing package.

See the documentation for more details.

Linker output no longer hidden by default

rustc invokes a linker on behalf of users. Historically, rustc has silenced linker output by default if the link completes successfully. This can mask real problems, though, so in Rust 1.97 we are enabling linker messages by default. These are emitted as a warning lint, for example:

warning: linker stderr: ignoring deprecated linker optimization setting '1'
  |
  = note: `#[warn(linker_messages)]` on by default

Common linker messages that have been diagnosed as false positives or intentional behavior are filtered out by rustc. Several defects have already been fixed as a result of no longer hiding this output on nightly.

Note that currently, linker_messages is a special lint that is not affected by the warnings lint group. This is intentional as rustc generally doesn't control linker output as precisely, and it's not uncommon for output to only appear on some platforms. If you are seeing what you think is a false positive output from the linker, please file an issue.

To silence the warning in the mean time, you can configure the lint level to allow. This can be done through Cargo.toml by adding a lints section like this:

[lints.rust]
linker_messages = "allow"

Stabilized APIs

• Default for RepeatN
• Copy for ffi::FromBytesUntilNulError
• Send for std::fs::File on UEFI
• <{integer}>::isolate_highest_one
• <{integer}>::isolate_lowest_one
• <{integer}>::highest_one
• <{integer}>::lowest_one
• <{uN}>::bit_width
• NonZero<{integer}>::isolate_highest_one
• NonZero<{integer}>::isolate_lowest_one
• NonZero<{integer}>::highest_one
• NonZero<{integer}>::lowest_one
• NonZero<{uN}>::bit_width

These previously stable APIs are now stable in const contexts:

• char::is_control

Other changes

Check out everything that changed in Rust, Cargo, and Clippy.

Contributors to 1.97.0

Many people came together to create Rust 1.97.0. We couldn't have done it without all of you. Thanks!

09 Jul 2026 12:00am GMT