This feature request also came up in the WECG: https://github.com/w3c/webextensions/issues/1039 Recently we added support for the sandbox key in manifest.json (bug 1685123). Such pages do not have special extension capabilities, so in theory it would be safe to expose crossOrigin-isolated APIs such as SharedArrayBuffer there. We could consider adding a flag to support COOP/COEP in such documents, if we are far away from such support in regular extension documents.
Bug 1673477 Comment 20 Edit History
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This feature request also came up in the WECG: https://github.com/w3c/webextensions/issues/1039 Recently we added support for the sandbox key in manifest.json (bug 1685123). Such pages do not have special extension capabilities, so in theory it would be safe to expose crossOrigin-isolated APIs such as SharedArrayBuffer there. We could consider adding a flag to support COOP/COEP in such documents, if we are far away from such support in regular extension documents. Note: [crossOriginIsolated](https://developer.mozilla.org/en-US/docs/Web/API/Window/crossOriginIsolated) implies separate browsing context groups. That would rule out the possibility of embedding a sandboxed page in the background page, at best an extension can only open a sandboxed extension page in a new tab and interact with it.