You may want to consider a macro script such as provided by autohotkey.
You can set a script to open a window, wait a while and then close it, or close it after a certain response. This one starts ie, waits 5 seconds and then closes the window even if something else took focus in between.
#Persistent winset,alwaysontop,on run, iexplore.exe htp: // localhost/cron.php sleep,5000 WinActivate,My Cron Results Page #match the page Title here WinClose,My Cron Results Page #match the page Title here
Using the Command Line Process Viewer/Killer/Suspender for Windows NT/2000/XP (type this into your favorite search engine), you could simply kill the process with "process -k firefox.exe" or "process -k iexplore.exe"