When we enable the WebExtension part of the screenshots system add-on, we see Jetpack test failures due to leaks: https://treeherder.mozilla.org/logviewer.html#?job_id=94848421&repo=try&lineNumber=5056 [tINFO - TEST-PASS | jetpack-package/addon-sdk/source/test/leak/test-leak-event-dom-closed-window.js.test sdk/event/dom does not leak when attached to closed window | should see at least one new window WARNING - TEST-UNEXPECTED-FAIL | jetpack-package/addon-sdk/source/test/leak/test-leak-event-dom-closed-window.js.test sdk/event/dom does not leak when attached to closed window | Component returned failure code: 0x8057000a (NS_ERROR_XPC_BAD_CONVERT_NATIVE) [xpcIJSWeakReference.get] INFO - TEST-INFO | Traceback (most recent call last): INFO - File "resource://gre/modules/Promise-backend.js", line 806, in walkerLoop INFO - this.handlers.shift().process(); INFO - File "resource://gre/modules/Promise-backend.js", line 925, in process INFO - nextValue = this.onReject.call(undefined, nextValue); INFO - File "resource://gre/modules/commonjs/sdk/test/assert.js", line 88, in fail INFO - this._log.fail(message); INFO - File "resource://gre/modules/commonjs/sdk/deprecated/unit-test.js", line 104, in fail INFO - this.console.testMessage(false, false, this.test.name, message); INFO - File "resource://gre/modules/commonjs/sdk/test/harness.js", line 541, in testMessage INFO - this.trace(); This is all platforms, both opt and debug. It could also be related to bug 1360512.

I've re-done a try build, and this is no longer an issue. Probably due to the recent webextension improvements.