The problem isn't that opening on mouse-up is worse, it's that it's different. After using an operating system for thousands of hours, one becomes accustom to t

The problem isn't that opening on mouse-up is worse, it's that it's different. After using an operating system for thousands of hours, one becomes accustom to the behavior of the standard controls. Anything that deviates from them and is not in widespread use - even if it is technically an improvement - will feel uncomfortable and "wrong". In some cases, like upgrading from Snow Leopard to Lion or Windows XP to Windows 7, the users adapt to the change. This is not likely to happen for a Javascript contro that is not in use on any major sites.