Add browser support where eval is not allowed by CSP

[mihaicodrean]

How about enhancing this:
var globalEval = eval, global = globalEval('this');
to this:
var globalEval = eval, global = typeof window !== 'undefined' ? window : globalEval('this');
I can create a pull request if that helps adoption.

[mihaicodrean]

To further clarify, eval() is no longer allowed in Thunderbird add-ons, for example.