Check your Firefox .torrent preferences

1. Edit > Preferences
2. Applications tab
3. Find "BitTorrent seed file" and click the dropdown to the right.
4. Choose 'Always ask'

Install and Configure the "Save Link in Folder" Add-on

1. Download and install [1] Save Link in Folder
2. Go to Tools > Add-ons
3. Find and select "Save Link in Folder", then click "Preferences"
4. Under "Main", click "New" (top right)
   1. Description: "BitTorrent"
   2. Path (wherever you like)
   3. if there is a duplicate filename... "Overwrite the file"

Final steps

1. Surf and find a .torrent file to download. Click on it.
2. In this dialogue, choose the new option "Save link in folder" and choose "BitTorrent".
   1. Unfortunately, the "Do this automatically for files like this from now on." does not work.

From now on, simply clicking on a .torrent file will pull up the 'save as' dialogue. Just press enter.

BUG: Unfortunately this same dialogue appears for other files. When you choose another option when saving that non-torrent file, you'll have to re-choose the "BitTorrent" option when downloading your next .torrent. Sigh.