Cross-origin isolation enables a web page to use powerful features such as
SharedArrayBuffer. An extension can opt into cross-origin isolation by specifying the appropriate values for the
cross_origin_opener_policy manifest keys. For example, a manifest like the one below will opt the extension's origin into cross-origin isolation.
"name": "CrossOriginIsolation example",
Opting into cross-origin isolation allows the extension to use powerful APIs like SharedArrayBuffers in its cross-origin isolated contexts. However, it does also come with certain side-effects. See Making your website "cross-origin isolated" using COOP and COEP for more information on this.
Even if an extension opts into cross-origin isolation, not all extension contexts will be cross-origin isolated. For example, cross-origin isolation is not fully implemented for service and shared workers currently. Similarly, a cross-origin isolated extension's web-accessible subframe on a regular web page is not considered cross-origin isolated currently.