When a frameDetached event comes soon after a frameAttached event, we hit an error in the ExecutionContext ctor:

1593123819052	RemoteAgent	TRACE	<-(connection {7635a878-adcd-984e-bce0-9a83387f1cea}) {"sessionId":1,"method":"Page.frameAttached","params":{"frameId":"6442450945","parentFrameId":"18","stack":null}}
1593123819053	RemoteAgent	TRACE	<-(connection {7635a878-adcd-984e-bce0-9a83387f1cea}) {"sessionId":1,"method":"Page.frameStartedLoading","params":{"frameId":"6442450945"}}
1593123819054	RemoteAgent	TRACE	<-(connection {7635a878-adcd-984e-bce0-9a83387f1cea}) {"sessionId":1,"method":"Page.lifecycleEvent","params":{"frameId":"6442450945","name":"init","timestamp":1593123819.051}}
1593123819056	RemoteAgent	TRACE	<-(connection {7635a878-adcd-984e-bce0-9a83387f1cea}) {"sessionId":1,"method":"Page.frameNavigated","params":{"frame":{"id":"6442450945","parentId":"18","url":"","name":"","securityOrigin":null,"mimeType":null}}}
1593123819057	RemoteAgent	TRACE	<-(connection {7635a878-adcd-984e-bce0-9a83387f1cea}) {"sessionId":1,"method":"Runtime.executionContextCreated","params":{"context":{"id":15,"origin":"","name":"","auxData":{"isDefault":true,"frameId":"6442450945","type":"default"}}}}
1593123819060	RemoteAgent	TRACE	<-(connection {7635a878-adcd-984e-bce0-9a83387f1cea}) {"sessionId":1,"method":"Network.responseReceived","params":{"requestId":"99574521791062","timestamp":1593123819.059,"type":" ... remotePort":80,"fromDiskCache":false,"protocol":"http/1.1","securityDetails":null,"securityState":"unknown"},"frameId":"18"}}
1593123819062	RemoteAgent	TRACE	<-(connection {7635a878-adcd-984e-bce0-9a83387f1cea}) {"sessionId":1,"method":"Network.responseReceived","params":{"requestId":"99574521791062","timestamp":1593123819.062,"type":" ... "remotePort":80,"fromDiskCache":true,"protocol":"http/1.1","securityDetails":null,"securityState":"unknown"},"frameId":"18"}}
1593123819284	RemoteAgent	TRACE	<-(connection {7635a878-adcd-984e-bce0-9a83387f1cea}) {"sessionId":1,"method":"Page.frameDetached","params":{"frameId":"6442450945"}}
1593123819284	RemoteAgent	TRACE	<-(connection {7635a878-adcd-984e-bce0-9a83387f1cea}) {"sessionId":1,"method":"Page.frameStartedLoading","params":{"frameId":"6442450945"}}
1593123819285	RemoteAgent	TRACE	<-(connection {7635a878-adcd-984e-bce0-9a83387f1cea}) {"sessionId":1,"method":"Page.lifecycleEvent","params":{"frameId":"6442450945","name":"init","timestamp":1593123819.284}}
console.error: 
  TypeError: can't access property "browsingContext", debuggee.docShell is null: ExecutionContext@chrome://remote/content/domains/content/runtime/ExecutionContext.jsm:53:5
_onContextCreated@chrome://remote/content/domains/content/Runtime.jsm:396:21
_onScriptLoaded@chrome://remote/content/domains/content/Page.jsm:324:15
emit@resource://gre/modules/EventEmitter.jsm:160:20
handleEvent/<@chrome://remote/content/observers/ContextObserver.jsm:90:16

This is the top error in gutenberg tests; >10% of tests are affected. Frames are attached/detached in quick succession as a result of key/mouse interactions. For example, quote.test.js.

(In reply to Maja Frydrychowicz :maja_zf (UTC-4) (maja@mozilla.com) from comment #1)

This is the top error in gutenberg tests; >10% of tests are affected. Frames are attached/detached in quick succession as a result of key/mouse interactions. For example, quote.test.js.

Clarification: tests that were previously passing now fail. Probably related to Bug 1599773 or Bug 1593226.

It also seems strange that we see Page.frameStartedLoaded and an init lifecycle event after the frame is detached. As far as I can tell from Chrome logs, after a frameDetached event there are never any more events for that frame id.

We have an overlap here:
https://searchfox.org/mozilla-central/rev/31d8600b73dc85b4cdbabf45ac3f1a9c11700d8e/remote/domains/content/Page.jsm#280-289

Maybe it's the wrong place to emit the events here, and we need a better DOM event?