Can't use official apis

[Zawardo1000]

I'm making a js action script to do some stuff during a filter. But i don't understand how to use the webextension apis... i saw filtaquilla already have a messenger defined: let messenger = Cc["@mozilla.org/messenger;1"].createInstance(Ci.nsIMessenger);

but when i try to access the api (example: messenger.folders.*) the api is undefined. What am i missing?