Install.addFile

The Install object's addFile method is the standard way to queue files for installation.

var xpiSrc = "file.txt";
initInstall(
  "Adding A File",
  "testFile",
  "1.0.1.7",
  1);
f = getFolder("Program");
setPackageFolder(f);
addFile(xpiSrc);
if (0 == getLastError())
   performInstall();
else
   cancelInstall();