I don't think Firefox is aware of what is happening in your PHP code on the server; it just gets an HTTP response or it doesn't. Can you post a simplified test case demonstrating the re-request behavior?

it works with IE8 and chrome. but with firefox always looping. HTTP response without re-entering a loop. shel_exec run the tsm client retrieve script.

Can you test in a new Firefox profile. In addition to bypassing current add-ons and custom settings, it should have completely fresh settings databases and a fresh cache folder.

Close Firefox and start up in the Profile Manager as described in "Profile Manager - Create, remove or switch Firefox profiles". Any time you want to switch profiles, close Firefox and return to this dialog.

Do you see any change in the behavior?

nothing changed. and I tried with another PC and also nothing changed

Can you post a simplified test case demonstrating the re-request behavior, or a link to the actual problem page?

actual problem page is in LAN. shel_exec run the ibm tsm client retrieve script.