Thunderbird Webextensions .messages.getFull() raises Exception 0x80004005 (NS_ERROR_FAILURE)

This is a kind of follow-up of the following question/answer: https://stackoverflow.com/a/60246205/6342243

The code at the end of this question gets a list of accounts, selects the emailAccountName, gets a MessageList object from the wantedMailFolderType and tries to get a MessagePart object from just one single messageId via browser.messages.getFull( messageId ) which always fails with the following Exception message:

[Exception... 
"Component returned failure code: 0x80004005 (NS_ERROR_FAILURE) 
[nsIMsgMessageService.streamMessage]"
nsresult: "0x80004005 (NS_ERROR_FAILURE)"
location: "JS frame :: resource:///modules/gloda/mimemsg.js
                    :: MsgHdrToMimeMessage
                    :: line 238"  data: no]
                       mimemsg.js:238:16

This behaviour is the same on linux mint 19.3 (64-Bit) running thunderbird 68.4.1 (64-Bit) as well as on windows 7 (64-Bit) running thunderbird 68.2.2 (32-Bit).

Here the code which reproduces the error:

emailAccountName     = "firstname.lastname@email.com";
wantedMailFolderType = "trash";

console.log( tstamp() + " Entered Main Program" );
function tstamp () {
    let d =new Date();
    return "" + d.getMinutes() + ":" + d.getSeconds() + "." + d.getMilliseconds();
}

function accountsList_successCallback( arrayOfMailAccount ) {
    console.log( tstamp() + " Entered accountsList_successCallback()" );
    let accountId = false;
    for (let i = 0; i < arrayOfMailAccount.length; i++) {
    if ( arrayOfMailAccount[i].name == emailAccountName ) {
        accountId  = arrayOfMailAccount[i].id;
        break;
        }
    }
    console.log( tstamp() + " Leaving accountsList_successCallback(), returning accountId: " + accountId );
    return accountId;
}
function mailAccount_successCallback( mailAccount ) {
    console.log( tstamp() + " Entered mailAccount_successCallback()" );
    let mailFolder = false;
    for (let i = 0; i < mailAccount.folders.length; i++) {
    if ( mailAccount.folders[i].type == wantedMailFolderType ) {
        mailFolder = mailAccount.folders[i];
        break;
        }
    }
    console.log( tstamp() + " Leaving mailAccount_successCallback(), returning mailFolder: " + mailFolder.type );
    return mailFolder;
}
async function getMessagesList( mailFolder ) {
    console.log( tstamp() + " Entered getMessagesList()" );
    let page = await browser.messages.list( mailFolder );
    let messageHeader = page.messages[ 0 ];
    let messageId     = messageHeader.id;
    console.log( `Trying to .getFull( messageId == ${messageId} ) MessagePart object now...` );
    let messagePart = await browser.messages.getFull( messageId );
    console.log( tstamp() + " Leaving getMessagesList()" );
}

browser.accounts.list()
    .then( accountsList_successCallback)  // after .accounts.list() Promise is fulfilled...
                                          // accountsList_successCallback is called, which
                                          // in this example returns the accountId string...
    .then( accountId => browser.accounts.get( accountId ))
    .then( mailAccount_successCallback)   // after .accounts.get() Promise is fulfilled...
                                          // mailAccount_successCallback is called, which
                                          // returns the wanted MailFolder...
    .then( getMessagesList )              // ... passed to getMessagesList(), which successfully
                                          // awaits a MessageList object...
                                          // but every call to .getFull( messageId ) fails.
    .catch( finalCatch )
;

function finalCatch( error ) {
    console.error( "ERROR passed to finalCatch() : " + error);
}

console.log( tstamp() + " Leaving Main Program" );

This was the output of the last run (line-numbers in popup.js xx-ed out, because they do not match with this extract):

52:40.859 Entered Main Program                                                   popup.js:xx:9
52:40.874 Leaving Main Program                                                   popup.js:xx:9
52:40.964 Entered accountsList_successCallback()                                 popup.js:xx:13
52:40.964 Leaving accountsList_successCallback(), returning accountId: account26 popup.js:xx:13
52:40.988 Entered mailAccount_successCallback()                                  popup.js:xx:13
52:40.989 Leaving mailAccount_successCallback(), returning mailFolder: trash     popup.js:xx:13
52:40.989 Entered getMessagesList()                                              popup.js:xx:13
Trying to .getFull( messageId == 1 ) MessagePart object now...                   popup.js:xx:13
[Exception...
 "Component returned failure code: 0x80004005 (NS_ERROR_FAILURE)
 [nsIMsgMessageService.streamMessage]"
  nsresult: "0x80004005 (NS_ERROR_FAILURE)"
  location: "JS frame :: resource:///modules/gloda/mimemsg.js
                      :: MsgHdrToMimeMessage
                      :: line 238"  data: no]
                         mimemsg.js:238:16
ERROR passed to finalCatch() : Error: An unexpected error occurred               popup.js:xx:13

Could anyone please try this out on his machine? How to proceed further? Should a bug on BugZilla be reportet?

Thanks in advance. richard

The problem is solved!

The exception was raised as long as and only while there was another login to the same IMAP-Account on another PC active. It seems that as long as there is more than one login or session simultaneously to the same Email-Account, the exception is raised.

Sorry for disturbing.

Thank you very much for your attention. richard