The polyfill detects the environment. If browser exists (Firefox), it does nothing. If only chrome exists (Chrome), it wraps all chrome.* callbacks into Promises.
The browser extension ecosystem has historically been fragmented. For years, developers built specifically for Chrome, often treating other browsers as an afterthought. However, the landscape has shifted. With Mozilla Firefox maintaining a loyal and privacy-conscious user base, and with browsers like Microsoft Edge and Opera adopting similar architectures, the return on investment for porting your extension has never been higher.
In Chrome, the extension ID is generated automatically based on the package signature. In Firefox, if you do not specify an ID, it will be generated randomly every time you load the temporary extension during development. This breaks storage.sync and message passing. Defining the ID here ensures consistency.
: Upload your .crx file to Mozilla’s ExtensionTest to receive a detailed report on errors or warnings specific to Firefox's environment.