I think you'll need to post the code before we can help you. It's not at all clear (to me at least), what you mean by:

I have created a module with a function that reads in the potentially very large file, and creates an html file displaying the results of the file. Next I do a redirection to the results. My main script calls this module via a thread, and detaches the thread. then the main script keeps refreshing the browser.

Particularly the highlighted bit? Words are never a good substitute for the code.

side question: Is it necessary to detach a thread whenever you don't intend to wait for it to finish before the script ends? Like would it automatically run till the end even tho the main script has finished executing?

When your main thread terminates, all other threads, regardless of whether they are detached or not, will terminate also. Usually with a message like: "Perl exited with N threads still running".

Although, the latest incarnation on the threads has (wrongly, IMO) suppressed this message in the case of detached threads. They now die silently!

Simply put. Your script cannot terminate and leave threads running. When the script dies, the threads die, regardless of their state.

The fact that you say; "My main script calls this module via a thread, and detaches the thread. then the main script keeps refreshing the browser." suggests to me that you are getting confused between threading and forking, but that would be clarified if you would post the code.