This linter verifies if a file has a known license header.

By default, Firefox uses MPL-2 license with the appropriate headers. In some cases (thirdpardy code), a file might have a different header file. If this is the case, one of the significant line of the header should be listed in the list of valid licenses.

Run Locally

This mozlint linter can be run using mach:

$ mach lint --linter license <file paths>


This linter is enabled on most of the whole code base.


This linter provides a --fix option. The python script is doing the change itself and will use the right header MPL-2 header depending on the language. It will add the license at the right place in case the file is a script (ie starting with !# or a XML file <?xml>).