Plugin works in jpm, but not after being built

Question

I have a very simple plugin which injects JavaScript into every webpage the user visits. The plugin works flawlessly whenever I run jpm on it. But the moment I build the plugin and test it in other Firefox browsers, (mine and friends) the plugin does not work.

Here's the simple code:

var pageMod = require("sdk/page-mod");

pageMod.PageMod({
  include: "*",
  contentScript: '(function() { console.log("This out\'a be working!"); })();'
});