Short description of issue
In Firefox, the theme editor injects a duplicate into the preview iframe, which breaks all module (@theme/*) imports. Reproduces on Horizon. Live storefront and other browsers are fine.
Reproduction steps
- Open an import-map-based theme (e.g. Horizon) in the theme editor using Firefox.
- Open DevTools → inspect the preview iframe’s .
- Observe two identical theme elements in the iframe document.
- Check the Console.
Additional info
Expected: One import map in the preview document, module imports resolve normally (as on the live storefront).
Actual: The preview iframe contains a duplicated theme import map. Firefox strictly enforces “one import map per document”, so the duplicate invalidates resolution and the console floods with: Uncaught TypeError: The specifier “@theme/component” was a bare specifier, but was not remapped to anything.…for every bare specifier (@theme/component, @theme/events, @theme/animation, etc.), killing the theme’s JS inside the editor.
Root cause: The editor re-injects the layout (including the import map) into the preview iframe during live rendering, producing a second import map. Firefox rejects it; Chrome/Edge/Safari tolerate it (so Firefox-only).
What type of topic is this
Bug report
