How to kill a single thread from Terminal in Ubuntu?

I'm new to Ubuntu and new here. I need to know this.

How do I kill a single thread from Terminal in Ubuntu? I have mozilla opened and it has 45 threads. I want to kill one of it.

I've already search many sources online but to no avail. Can anyone help me?

You can't. Not without killing the whole process. From man 3 pthread_kill, a function used for signal handling:

NOTES
   Signal dispositions are process-wide: if a signal handler is installed,
   the  handler  will  be  invoked  in  the  thread  thread,  but  if  the
   disposition  of  the signal is "stop", "continue", or "terminate", this
   action will affect the whole process.

Also see this U&L post.