This revision makes changes to files both inside and in files outside of it. The New Tab page for Firefox Desktop supports train-hopping — a mechanism that allows New Tab code to be deployed to Beta and Release channels independently of the standard release train. Cross-layer changes can break train-hop compatibility, which may block New Tab deployments until fixes reach Release through normal channels.

If your change modifies platform code that browser/extensions/newtab depends on (such as module URIs, DOM APIs, or Nimbus feature definitions), please check whether a compatibility shim is needed. Shims should be marked with a comment indicating the Firefox version that must reach Release before the shim can be removed.

If your change is unrelated to the New Tab page's train-hop compatibility (for example, it only touches tests or documentation), you can possibly disregard this message - but if you are unsure whether your change affects train-hop compatibility, please ensure that someone from the home-newtab-reviewers-rotation review group has a chance to review before landing.