We Can open as many as browser in QTP using Vb script at once 
as:
Write the Below code in text pan & Click Run

for i=1 to 5
  Systemutil.run"firefox.exe"

Next

Give URLs in URLS.txt documents and save 

Set a= createobject("scripting.filesystemobject")
set b=a.opentextfile("c:\ray\URLS.txt",1,true)
 i=1
Do while not b.atendofstream
c= b.readline
systemutil.Run"iexplore"
browser("name:=Google").Navigate c
browser("text:=.*").WaitProperty "text",c,10000
loop


Or else try with it


Set a= createobject("scripting.filesystemobject")
set b=a.opentextfile("c:\ray\URLS.txt",1,true)
 i=1
Do while not b.atendofstream
c= b.readline
i=i+1
systemutil.Run c
browser("text:=.*").WaitProperty "text",c,10000
loop