I have read this thread, and some other How to run a local exe in my firefox extension The problem is, at deployment and using firefox 4.0.1, if I install the .xpi extension, the xpi is put inside the \Profiles...\extensions as **.xpi, which is a compressed format All the solutions assume that the the extension is put in a folder, thus they are accessing the folder as is, which I cannot do for example this guy says //**** get profile folder path **** var dsprops = Components.classes['@mozilla.org/file/directory_service;1'] .getService(Components.interfaces.nsIProperties); var ProfilePath = dsprops.get("ProfD", Components.interfaces.nsIFile).path; //**** initialize file **** var file = Components.classes["@mozilla.org/file/local;1"] .createInstance(Components.interfaces.nsILocalFile); file.initWithPath(ProfilePath); //**** append each step in the path **** file.append("extensions"); file.append("guid"); file.append("sample.exe"); guid in my case is installed as {f13b157f-b174-47e7-a34d-4815ddfdfeb8}.xpi which cannot be accessible this way