Incremental builds with filesystem watching

Note: This page covers required steps to incrementally update a bleeding-edge, development version of Firefox for Desktop. We use watchman to monitor filesystem changes and automatically generate the changed build outputs.

If you're having difficulty following this documentation, or hit a roadblock, please contact:

This not only helps us solving your difficulty, but often those who come after you.  For more information, see the general Firefox build documentation.

Incremental builds with filesystem watching

Firefox for Desktop supports a fast build build modem called artifact mode.  When you're using artifact mode, you can opt-in to an even faster incremental front-end build process.


You must:

  • Be using artifact builds.
  • Be building Firefox for Desktop.
  • Have successfully built Firefox for Desktop.
  • Have watchman installed.

Installing pywatchman

Incremental front-end builds require the pywatchman wrapper around watchman to be installed.  To verify that you have watchman installed, ensure that watchman --version succeeds.

Most Desktop developers on Mac OS X or Linux should find:

./mach watch

just works.  This incrementally rebuilds local JS, CSS, and packaged files, including images.

Windows developers may have a more difficult time.  We're working on smoothing out the kinks for Windows developers, and would appreciate working through problems with you.

Quick Restart workflow

mach watch and the developer-only Quick Restart key binding reduces the time of each edit-compile-run cycle.  In a terminal, run

./mach build # (Capture changes to the build system -- only needed once!)
./mach watch

And in a second terminal, run

./mach run

Here's an example of using Quick Restart to replace the current browser process with one reflecting changes to browser/components/customizableui/CustomizeMode.jsm:

Screen capture that shows using Quick Restart to replace the current browser process with one reflecting changes to browser/components/customizableui/CustomizeMode.jsm


Things that are supported

  • Modifying JavaScript, (X)HTML, CSS resources, string properties and DTD files.

Most things updated by mach build faster should also work with mach watch.

Things not supported

  • Modifying build system configuration and definitions, including definitions and manifests.  Kill mach watch, run mach build faster to pick up the changes to the build system itself, and restart mach watch.


Discussion are best started on the dev-builds mailing list.  Raise questions in #build on IRC.  File bugs in Core :: Build Config, blocking bug 1384241.

Document Tags and Contributors

 Contributors to this page: nalexander, bunnybooboo
 Last updated by: nalexander,