Cross-browser incompatibility, how to put the button "同意して、アカウントを作成します" back into the big box?

If you visit http://www.tenxian.com/jp/common/signup.php? with Firefox, you will find that the button "同意して、アカウントを作成します" is out of the box; if you access this web page with IE, then there is no problem. How to fix this problem(put "同意して、アカウントを作成します" back into the box in Firefox开发者_如何学Python)?

Remove the height on the .signup in your CSS.