Changes in Thunderbird 74

legacy

• The legacy API has been removed. This has been covered elsewhere.

accounts/folders

• The MailFolder object gained a subFolders property. From now on the accounts API functions will return a hierarchy of folders instead of a flat list. If you still need a flat list you should traverse the folder hierarchy:

  browser.accounts.list().then(accounts => {
    let arrayOfFolders = [];
  
    function traverse(folders) {
      if (!folders) {
        return;
      }
      for (let f of folders) {
        arrayOfFolders.push(f);
        traverse(f.subFolders);
      }
    }
  
    for (let account of accounts) {
      traverse(account.folders);
    }
    return arrayOfFolders;
  });
  

  This example code works with both the current API in 68 and the new version in 74 (which will be backported to 68 after some time in beta).

compose

• The compose API gained two new functions and an event. The getComposeDetails and setComposeDetails functions let you retrieve or change the recipients and subject of a message being composed. More details will be added later. The onBeforeSend event is fired when a message is about to be sent. At this point your extension can prevent sending or change the same details as in the new functions.

messages

• The query function can now query by tags.

• The MessageHeader object now has junk properties: junkScore is an integer score from 0 (not spam) to 100 (spam). junk shows whether or not that score is greater than the junk threshold.

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Bugzilla list of fixed WebExtension API defects in Thunderbird 74.