thunderbird bug accessing to tab with messenger.messageDisplay.getDisplayedMessage

Question

I am trying to access the content of a tab. But most of the time it gives an error. Has the code ever worked?

list of tabs:

messenger.tabs.query(
  {
    active: false ,
    currentWindow: true
  }
).then( (tabs) => { console.log (tabs); })

then:

messenger.messageDisplay.getDisplayedMessage(4).then ((msn) => {
 console.log(msn);
});

enter image description here but 99% msn is null.

Please see the attach files

thanks!!!!

enter image description here