You can use DP. If you know which browser to close, for ex: creation time, title, opentitle then it becomes easy to pinpoint to that particular browser.
set mybrow = description.create()
'mybrow("title").value = ".*xyz.*" ' contains a xyz in the title
mybrow("CreationTime").value = "0" ' Opens 1st opened browser
if browser(mybrow).GetROProperty("title") = "what you expect" then
browser(mybrow).close
end if
mybrow("CreationTime").value = "1" ' Opens 2nd opened browser
if browser(mybrow).GetROProperty("title") = "what you expect" then
browser(mybrow).close
end if
Depending on which title you want to close