Fix SW packaging in web extensions (#8424)

Author: olistic

packages/packagers/webextension/src/WebExtensionPackager.js

@@ -23,6 +23,13 @@ export default (new Packager({
       relativeBundlePath(bundle, b, {leadingDotSlash: false});
 
     const manifest = JSON.parse(await asset.getCode());
+
+    if (manifest.background?.type === 'module') {
+      // service workers are built with output format 'global'
+      // see: https://github.com/parcel-bundler/parcel/blob/3329469f50de9326c5b02ef0ab1c0ce41393279c/packages/transformers/js/src/JSTransformer.js#L577
+      delete manifest.background.type;
+    }
+
     const deps = asset.getDependencies();
     const war = [];
     for (const contentScript of manifest.content_scripts || []) {