R: ESS shell.exec speed

I am using ESS in Windows XP. I have noticed that 开发者_如何学Goshell.exec is much slower with ESS than with RGui (the problem occurs when I try help(ls) for example, the help is displayed much faster in RGui, I tracked it down and it is due to shell.exec). Is there any reason for this? How can I fix it? My default browser is Firefox.