spoofWindowSize does not work outside Twitter

[hankhplee]

After testing out spoofWindowSize a bit more, I found two issues with the current solution:

1. the feature works only on Twitter; I haven't understood why it does not work on Facebook, LinkedIn, and YouTube; the feature also messes up the hamburger menu of these sites.
2. Object.prototype.defineGetter() is now deprecated; may consider change it to Object.defineProperty().