Manifest V3 migration problem Firefox need a page which loads a script : "background": { "page": "background-page.html" }, where chrome works with service_worker : "background": { "service_worker": "background.js", "type": "module" }, Links : https://stackoverflow.com/questions/75043889/manifest-v3-background-scripts-service-worker-on-firefox https://extensionworkshop.com/documentation/develop/manifest-v3-migration-guide/#browser-action