diff -r 000000000000 -r 6474c204b198 toolkit/devtools/sourcemap/UPGRADING.md
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/devtools/sourcemap/UPGRADING.md	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,12 @@
+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
+    $ git co source-map
+    $ git co <latest-tagged-version>
+    $ npm run-script build
+    $ cp dist/SourceMap.jsm /path/to/mozilla-central/toolkit/devtools/sourcemap/SourceMap.jsm
+    $ cp dist/test/* /path/to/mozilla-central/toolkit/devtools/sourcemap/tests/unit/
+