I just took a look at the generated code and here is the solution. This simple modification in AGKPlayer.js will open the requested URL in the same window so it will not trigger the pop-up blocker and is exactly what you were trying to achieve.
1.) Open AGKPlayer.js
2.) Do a search for:
_blank
3.) Replace
_blank with
_self
4.) Save the file, reupload it to your server replacing the existing one, and then press
CTRL+F5 on the page to clear the cache to ensure the latest JavaScript version is loaded.
That is it. Now when OpenBrowser() is called the page will replace the existing one. TGC should consider making this modification themselves as otherwise in every modern browser the requested page will likely be blocked due to how the function is called via the HTML5 AppGameKit context (which browsers see as non-user triggered).
EDIT: I've also confirmed a similar approach can be taken to easily communicate with externally defined JavaScript functions as well, which can be used to open a URL in a
new window/tab without triggering the pop-up block alert. This makes it easy to pass data to standard JavaScript and then perform any common functions there (alerts etc.) I may make a thread describing this in more detail at some point.