Here's the scenario: I download a .torrent file in firefox. Now I want that utorrent will be able to detect the folder where I save the .torrent file. And it will download it automatically without me setting it up.
First you should define your default download folder from uTorrent options:
When you click on a .torrent link, Firefox should automatically ask you what to do. Don't save the .torrent file, just select "Open with utorrent". Then the relevant files will be downloaded to the folder you set.