Set Transmission as the default handler for magnet links in Google Chrome.

gistfile1.md

Check that the file /usr/share/applications/transmission-gtk.desktop contains:

Exec=transmission-gtk %U
MimeType=application/x-bittorrent;x-scheme-handler/magnet;

Configure xdg-open to use Transmission: xdg-mime default transmission-gtk.desktop x-scheme-handler/magnet

In order to work properly function with openbox, replace generic with gnome, kde, xfce, or lxde in the file /usr/bin/xdg-open:

detectDE
if [ x"$DE" = x"" ]; then
DE=generic