Firefox MSIX packages are full participants in the “modern” Windows app packaging system. They are distributed, installed, updated, repaired, and uninstalled entirely using that system. This gives administrators lots of deployment options, and also grants complete control over when and how application updates are rolled out (Firefox’s built-in updater is always fully disabled in MSIX packages). This stands in contrast to Firefox MSI packages, which mostly work against the Windows Installer framework rather than with it, and therefore are missing a lot of important functionality; for example, tools that install MSI packages generally cannot uninstall Firefox 1. This means the MSIX package may well be the better option for deploying to Windows 10 and up.
repackage the ZIP packages produced by signed build tasks into MSIX
shippable-l10n variants depend on Linux64 builds and
localization tasks to produce signed langpacks, which are incorporated
into the MSIX package as distribution extensions. (This is the same
approach taken by
flatpak Linux packages.)
repackage-signing-shippable-l10n-msix tasks sign the MSIX packages
produced by the repackage tasks.
Signing in automation¶
MSIX packages are signed by the same certificates that sign binaries for
other jobs. In practice, this means that try builds are signed with the
`Mozilla Fake CA
In order to install try builds locally, you must trust this certificate.
For your own security, it’s best to do this in Windows Sandbox or a
Virtual Machine. To do so run the following in an elevated
$ Import-Certificate -FilePath "MozFakeCA_2017-10-13.cer" -Cert Cert:\LocalMachine\Root\ ... Thumbprint Subject ---------- ------- FA056CEBEFF3B1D0500A1FB37C2BD2F9CE4FB5D8 CN=Mozilla Fake CA
shippable-l10n MSIX variants incorporate signed langpacks. These
in turn are signed with the same certificate. Firefox knows about this
certificate but does not trust it by default. To trust it, set the
hidden Gecko boolean preference
Sadly, it’s not possible to set preferences via a
early enough to impact loading the signed langpacks (see Bug
once the signed langpacks fail to load once, they will not be reloaded
make testing the first-run experience challenging. What can be done is
to install the MSIX package (perhaps using
Add-AppxPackage -Path ...) and determine the profile directory
about:support). Uninstall the MSIX package (perhaps using
Get-AppxPackage | Where -Property Name -like "Mozilla.*" | Remove-AppxPackage).
Delete the contents of the profile directory entirely, but add a file
user_pref("xpinstall.signatures.dev-root", true); user_pref("extensions.logging.enabled", true);
Reinstall the MSIX package and the signed langpacks should now be loaded (slowly!) and available after first startup.
Local developer builds¶
mach repackage msix lets you repackage a Firefox package (or
directory) into an MSIX/App Package. The main complication is that an
App Package contains channel-specific paths and assets, and therefore
needs to be branding-aware, much as an Android package needs to be
The tool is designed to repackage ZIP archives produced in automation. Start looking for official builds at locations like:
Or package a local developer build with
mach package, and look for
Repackage using commands like:
$ ./mach repackage msix \ --input firefox-88.0.1.zip \ --channel=official \ --arch=x86_64 \ --verbose
Paths to tools can be set via environment variables. In order, searched first to searched last:
the tool name, like
C:/Program Files (x86)/Windows Kits/10
The repackaged MSIX files produced are not signed by default. In
automation, Mozilla’s signing service signs the repackaged MSIX files.
For local testing, you can sign them with a self-signed certificate by
mach repackage msix, or with commands like:
$ ./mach repackage sign-msix --input test.msix --verbose
Or sign them yourself following Microsoft’s self-signed certificate instructions.
Updating the MSIX template¶
MSIX is an “open format” in one sense: the MSIX container format is
specified at https://github.com/Microsoft/msix-packaging. It is
categorically not an open format in another sense: many of the
contained files are proprietary binary formats (
.reg – registry
hive files) or undocumented (
.pri files – resource index files).
Generally the MSIX packaging code tries to avoid requiring such files that can’t be built from sources. Where they are truly required, it tries to use a single such file independent of branding and other configuration, checked into the source tree.
Generate a new
resources.pri file on a Windows machine using
makepri.exe from the Windows SDK, like:
$ makepri.exe new \ -IndexName firefox \ -ConfigXml browser/installer/windows/msix/priconfig.xml \ -ProjectRoot browser/branding/official/msix \ -OutputFile browser/installer/windows/msix/resources.pri \ -Overwrite
The choice of channel (i.e.,
The MSI has to be limited in this way because of the difficulty of migrating existing installations into MSI and adding support for it to Firefox’s update pipeline. MSIX does not have these constraints, because the partially virtualized file system that these kinds of apps run in makes install migration impossible and unnecessary.