This is not a new problem, and I thought people would have worked out that fact by now.
This is almost always some kind of server issue. Look at your server's logs, see what it has to say on the topic. Look for any errors related to wp-admin. Make sure that you uploaded all the WordPress files correctly. Disable mod_security.
Whatever, but the point is that the error is not a browser error. They did indeed test it in all browsers. I've tested it on eight browsers on three platforms. Every part works in every one of them.
Until you accept that it's not a "bug" in the code but is instead some kind of issue on your specific setup, for your specific case, you'll never fix it. We can't help you until you accept that fact.