problem with xpinstall-getVersion

[MacTan]

Hi,

    I managed the install the xpi file using the following code. Later I
created a web page with a button, a click on iyt will call
InstallTrigger.getVersion('barley') and it always return null. Why?
I noticed that if the xpi file is installed and I called getVersion
immediately, it will return the version number correctly. restart the
browser again, click the button and getVersion() will return null again.
Why?

Thanks


var err = initInstall("barley v", "barley", "1.0.1.0");
logComment("initInstall: " + err);

addFile("Barley Grain",  "barley.jar",      // jar source folder
getFolder("Chrome"),        // target folder
  "");                        // target subdir

registerChrome(PACKAGE | DELAYED_CHROME, getFolder("Chrome","barley.jar"),
"content/");

if (err==SUCCESS)
  performInstall();
else
  cancelInstall(err);