The maximum number of top level extension items that can be added to a menu item whose
ContextType is "browser_action" or "page_action". Any items beyond this limit will be ignored.
Its value is
6 on Firefox and Chrome.
For compatibility with other browsers, Firefox makes this property available via the
contextMenus namespace as well as the
BCD tables only load in the browser
Note: This API is based on Chromium's
chrome.contextMenus API. This documentation is derived from
context_menus.json in the Chromium code.