# Side Panel [Chrome Docs](https://developer.chrome.com/docs/extensions/reference/sidePanel/) :::tip Chromium Only Firefox does not support sandboxed pages. ::: ## Filenames - `entrypoints/sidepanel.html` - `entrypoints/.sidepanel.html` - `entrypoints/sidepanel/index.html` - `entrypoints/.sidepanel/index.html` ## Definition Plain old HTML file. ```html Title ```