gecko-dev/devtools/shared/platform/README.md

This directory is treated specially by the loaders.

In particular, when running in chrome, a resource like "devtools/shared/platform/mumble" will be found in the chrome subdirectory; and when running in content, it will be found in the content subdirectory.

Outside of tests, it's not ok to require a specific version of a file; and there is an eslint test to check for that. That is, require("devtools/shared/platform/client/mumble") is an error.

When adding a new file, you must add two copies, one to chrome and one to content. Otherwise, one case or the other will fail to work.