JAR Manifests are plaintext files in the tree that are used to package chrome
.jar files and create Chrome Registration
manifests. JAR Manifests are commonly named
jar.mn. They are declared in
moz.build files using the
JAR_MANIFESTS variable, which makes up a collection of
All files declared in JAR Manifests are processed and installed into
omni.ja files in
toolkit/ when building Firefox.
jar.mn files are automatically processed by the build system when building a
source directory that contains one. The
jar.mn is run through the
Text Preprocessor before being passed to the manifest processor. In order to
@variables@ expanded (such as
@AB_CD@) throughout the file, add
#filter substitution at the top of your
The format of a jar.mn is fairly simple; it consists of a heading specifying which JAR file is being packaged, followed by indented lines listing files and chrome registration instructions.
Shipping Chrome Files¶
To ship chrome files in a JAR, an indented line indicates a file to be packaged:
<jarfile>.jar: path/in/jar/file_name.xul (source/tree/location/file_name.xul)
Note that file path mappings are listed by destination (left) followed by source (right).
Same Directory Omission¶
If the JAR manifest and packaged files live in the same directory, the source path and parentheses can be omitted.
A sample of a
jar.mn file with omitted source paths and parentheses is this revision of browser/components/colorways/jar.mn:
browser.jar: content/browser/colorwaycloset.html content/browser/colorwaycloset.css content/browser/colorwaycloset.js
Writing the following is equivalent, given that the aforementioned files exist in the same directory as the
jar.mn. Notice the
.jar file is named
browser.jar: content/browser/colorwaycloset.html (colorwaycloset.html) content/browser/colorwaycloset.css (colorwaycloset.css) content/browser/colorwaycloset.js (colorwaycloset.js)
This manifest is responsible for packaging files needed by Colorway Closet, including JS scripts, localization files, images (ex. PNGs, AVIFs), and CSS styling. Look at browser/components/colorways/colorwaycloset.html to see how a file may be referenced using its chrome URL.
The source tree location may also be an absolute path (taken from the top of the source tree). One such example can be found in toolkit/components/pictureinpicture/jar.mn:
toolkit.jar: * content/global/pictureinpicture/player.xhtml (content/player.xhtml) content/global/pictureinpicture/player.js (content/player.js)
Asterisk Marker (Preprocessing)¶
An asterisk marker (
*) at the beginning of the line indicates that the file should be processed by the Text Preprocessor before being packaged.
The file toolkit/profile/jar.mn indicates that the file toolkit/profile/content/profileDowngrade.xhtml should be
run through the preprocessor, since it contains
#endif statements that need to be interpreted:
* content/mozapps/profile/profileDowngrade.xhtml (content/profileDowngrade.xhtml)
Base Path, Variables, Wildcards and Localized Files¶
.jar file location may be preceded with a base path between square brackets.
The file toolkit/locales/jar.mn uses a base path so that the
.jar file is under a
which is a special directory parsed by mozbuild.
It is also named according to the value passed by the variable
@AB_CD@, normally a locale. Note the use of the preprocessor directive
#filter substitution at the top of the file for replacing the variable with the value:
#filter substitution ... [localization] @AB_CD@.jar: crashreporter (%crashreporter/**/*.ftl) toolkit (%toolkit/**/*.ftl)
The percentage sign in front of the source paths designates the locale to target as a source. By default, this is
en-US. With this specific example, /toolkit/locales/en-US would be targeted.
Otherwise, the file from an alternate localization source tree
/l10n/<locale>/toolkit/ is read if building a localized version.
The wildcards in
**/*.ftl tell the processor to install all Fluent files within the
toolkit directories, as well as their subdirectories.
Chrome Registration instructions are marked with a percent sign (
%) at the beginning of the
line, and must be part of the definition of a JAR file. Any additional percents
signs are replaced with an appropriate relative URL of the JAR file being
There are two possible locations for a manifest file. If the chrome is being
built into a standalone application, the
jar.mn processor creates a
<jarfilename>.manifest next to the JAR file itself. This is the default
USE_EXTENSION_MANIFEST = 1, the
creates a single
chrome.manifest file suitable for registering chrome as
The file browser/themes/addons/jar.mn registers a
resource chrome package under the name
builtin-themes. Its source files are in
browser.jar: % resource builtin-themes %content/builtin-themes/ content/builtin-themes/alpenglow (alpenglow/*.svg) content/builtin-themes/alpenglow/manifest.json (alpenglow/manifest.json)
Notice how other files declare an installation destination using the
builtin-themes resource that is defined. As such, a SVG file
preview.svg for a theme
Alpenglow may be loaded using the resource URL
so that a preview of the theme is available on
about:addons. See Chrome Registration for more details on
resource and other manifest instructions.