[xmonad] Why doesnot it jump to the browser when pressing URL in emacs-erc ?

[z_axis]

hi, friends
Using the same emacs config, clicking URL in emacs-erc under STUMPWM will  
open and jump to the browser(Opera). However, under XMONAD it just open  
the URL without switching the focus to the browser.
it is not a big problem but a bit uncomfortable.

Any suggestion is appreciated !