Fix breaking change to Firefox extensions

https://github.com/petkaantonov/bluebird/commit/e6bd2e014b36e0ab94b7ae204bd7a131e0e2f4f2#diff-026e6ee461445a75dbf07f09752148bd broke https://github.com/petkaantonov/bluebird/commit/efc82a11ffa9703bf3ceaf81432853206651b497 

In firefox extensions you can still access the global scope through window with `window.wrappedJSObject`. When we detect global - we now check for this.