performance improvement in plugins.js

Performance and speed are something important when it comes to javascript, so I think this little improvement to  the script in `plugins.js` will make sense.

I tested it with JSPerf: http://jsperf.com/testing-this-window-parameter
In every browser I tested, it seems to be a little bit faster.
Despite thhe context, who is going to execute the file more than 170k times to leverage ~6% improvement?