registering chrome

[Emiliano Heyns]

What is wrong with this:

const aomStartup = Cc["@mozilla.org/addons/addon-manager-startup;1"].getService(Ci.amIAddonManagerStartup);
 const manifestURI = Services.io.newURI(`${rootURI}manifest.json`);
 let chromeHandle = aomStartup.registerChrome(manifestURI, [
      ["icons", "zotero-open-pdf", "icons/"]
    ]);

I'm getting

Component returned failure code: 0x80070057 (NS_ERROR_ILLEGAL_VALUE) [amIAddonManagerStartup.registerChrome]

I'm using the same code in BBT where it does succeed (although BBT also loads FTLs, this plugin does not)