Actually, the logic behind killing the cookie at browser exit is that BES gets to re-detect the browser again. Because today the same browser may visit your link with a specific setup, the same day maybe the person decides to upgrade something (a plug-in or whatever), which the exploit doesn't necessarily support, which increases the risk of crashing because it assumes it's the same setup. When I wrote BES I never wanted to assume the same browser would always have the same setup. So that's why.

If you don't think that's a valid concern, let me know and maybe we can work something out.

Thanks!