old_contents: browser.WindowListener.registerChromeUrl([
    ["content",  "folderflags",          "chrome/content/"],
    ["locale",   "folderflags", "bg-BG", "chrome/locale/bg-BG/"],
    ["locale",   "folderflags", "cs-CZ", "chrome/locale/cz-CZ/"],
    ["locale",   "folderflags", "de",    "chrome/locale/de/"],
    ["locale",   "folderflags", "en-US", "chrome/locale/en-US/"],
    ["locale",   "folderflags", "es-ES", "chrome/locale/es-ES/"],
    ["locale",   "folderflags", "it",    "chrome/locale/it/"],
    ["locale",   "folderflags", "ja-JP", "chrome/locale/ja-JP/"],
    ["locale",   "folderflags", "pt-BR", "chrome/locale/pt-BR/"],
    ["locale",   "folderflags", "pt-PT", "chrome/locale/pt-PT/"],
    ["locale",   "folderflags", "sk-SK", "chrome/locale/sk-SK/"],
    ["locale",   "folderflags", "sr",    "chrome/locale/sr/"],
    ["locale",   "folderflags", "sv-SE", "chrome/locale/sv-SE/"],
    ["locale",   "folderflags", "zh-CN", "chrome/locale/zh-CN/"],
  ]);
  
  // For Thunderbird 78.0 and later
  browser.WindowListener.registerWindow(
    "chrome://messenger/content/folderProps.xhtml",
    "chrome://folderflags/content/folderProps.js");
  
  // For Thunderbird 68
  browser.WindowListener.registerWindow(
    "chrome://messenger/content/folderProps.xul",
    "chrome://folderflags/content/folderProps.js");
  
  browser.WindowListener.startListening();
  
new_contents: browser.WindowListener.registerChromeUrl([
    ["content",  "folderflags",          "chrome/content/"],
    ["locale",   "folderflags", "bg-BG", "chrome/locale/bg-BG/"],
    ["locale",   "folderflags", "cs-CZ", "chrome/locale/cz-CZ/"],
    ["locale",   "folderflags", "de",    "chrome/locale/de/"],
    ["locale",   "folderflags", "en-US", "chrome/locale/en/"],
    ["locale",   "folderflags", "es-ES", "chrome/locale/es-ES/"],
    ["locale",   "folderflags", "it",    "chrome/locale/it/"],
    ["locale",   "folderflags", "ja-JP", "chrome/locale/ja-JP/"],
    ["locale",   "folderflags", "pt-BR", "chrome/locale/pt-BR/"],
    ["locale",   "folderflags", "pt-PT", "chrome/locale/pt-PT/"],
    ["locale",   "folderflags", "sk-SK", "chrome/locale/sk-SK/"],
    ["locale",   "folderflags", "sr",    "chrome/locale/sr/"],
    ["locale",   "folderflags", "sv-SE", "chrome/locale/sv-SE/"],
    ["locale",   "folderflags", "zh-CN", "chrome/locale/zh-CN/"],
  ]);
  
  // For Thunderbird 78.0 and later
  browser.WindowListener.registerWindow(
    "chrome://messenger/content/folderProps.xhtml",
    "chrome://folderflags/content/folderProps.js");
  
  // For Thunderbird 68
  browser.WindowListener.registerWindow(
    "chrome://messenger/content/folderProps.xul",
    "chrome://folderflags/content/folderProps.js");
  
  browser.WindowListener.startListening();
  
subject: fix broken 1.4.1