Rather than make changes to the built files here, make them upstream and then upgrade our tree's copy of the built files. To upgrade the source-map library: $ git clone https://github.com/mozilla/source-map.git $ cd source-map $ git checkout <latest-tagged-version> $ npm install $ npm run-script build -or- nodejs Makefile.dryice.js (if you have issues with npm) $ cp dist/source-map.js /path/to/mozilla-central/devtools/shared/sourcemap/source-map.js $ cp dist/test/* /path/to/mozilla-central/devtools/shared/sourcemap/tests/unit/