I noticed that also, it is different from browser to browser.
you could try to detect the user agent (but there will be many cases where this is not correct) and then set the position if the game runns in this browser:
UserAgent
Return the full user agent string for the browser, e.g. Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.7 (KHTML, like Gecko) Chrome/16.0.912.63.
regards