firefox/testing/web-platform/tests/resources/chromium/README.md

This directory contains Chromium-specific test resources, including mocks for test-only APIs implemented with MojoJS.

Please do not copy *.mojom.m.js into this directory. Follow this doc if you want to add new MojoJS-backed mocks: https://chromium.googlesource.com/chromium/src/+/main/docs/testing/web_platform_tests.md#mojojs