gecko-dev/toolkit/devtools/sourcemap/UPGRADING.md

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/toolkit/devtools/sourcemap/source-map.js
$ cp dist/test/* /path/to/mozilla-central/toolkit/devtools/sourcemap/tests/unit/