by Mozilla Suggest Firefox extension developers started migrating from Manifest V2 to Manifest V3. Manifest V3 is a new extension system for Google Chrome, and the Chrome Web Store will phase out Manifest V2 extensions from January next year. Mozilla’s Manifest V3 is different from Chrome’s Manifest V3, including: Services Workers is not yet provided, Firefox uses Event Pages as background scripts, and the two may be used interchangeably depending on the function; declarativeNetRequest (DNR) is not provided, Firefox will retain the WebRequest API replaced by DNR – This is where the new extension system has sparked widespread controversy, with ad blocking extensions like uBlock Origin using WebRequest to block requests before ads are downloaded; storage.session API is not yet available.
https://blog.mozilla.org/addons/2022/10/31/begin-your-mv3-migration-by-implementing-new-features-today/
