In this function (devtools/server/actors/root.js#734-740 ), we iterate over this._tabDescriptorActorPool children, and call their removeActorByName.

The issue is that removeActorByName is a BrowsingContextTargetActor, and the children in _tabDescriptorActorPool should be TabDescriptors (devtools/server/actors/descriptors/tab.js#39) which don't have such method.

So if this is called, this is probably throwing.

So, this function is called from

• removeTargetScopedActor (devtools/server/actors/utils/actor-registry.js#342-347)
• which is called from unregisterModule (devtools/server/actors/utils/actor-registry.js#96-113)
• which only seems to be called by destroy (devtools/server/actors/utils/actor-registry.js#422-430 )
• which is called from DevToolsServer#destroy (devtools/server/devtools-server.js#148-164), where we close the connections
• and when a connections closes, it calls DevToolsServer._connectionClosed ([https://searchfox.org/mozilla-central/rev/f36cb2af46edd2659f446b7acdb2154e230ee445/devtools/server/devtools-server-connection.js#482])
• in which we remove the connection from the set of DevToolsServer connections (devtools/server/devtools-server.js#473)
• which means, the connections set is now empty, and since it's what we pass to the actor registery (devtools/server/devtools-server.js#129 ) we won't have anything to loop over

for (const connID of Object.getOwnPropertyNames(this._connections)) {  // this._connections is an empty object here

so what's inside the loop isn't called, and we don't see the underlying issue (calling a method that does not exist on tab descriptors)

it also appears to be called from

• unregisterActor (devtools/server/actors/utils/actor-registry-utils.js#75-94)
• which is called by ActorActor#unregister (devtools/server/actors/actor-registry.js#29-31 )

but I'm not sure if/how this is used from the client, I need to investigate a bit more