Firefox does not associate magnet links to Transmission

If you try to open a magnet link in thepiratebay, a Launch Application window will open asking to choose a torrent client, but there are no program in the list (take a look at the picture).

Why is it not configured to open Transmission? After all, it is the default torrent client in Ubuntu and other flavors, and for begginers users it is hard to realize that you can navigate to /usr/bin/ to find transmission in that Launch Application window.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: firefox 29.0+build1-0ubuntu0.14.04.2
ProcVersionSignature: Ubuntu 3.13.0-24.46-generic 3.13.9
Uname: Linux 3.13.0-24-generic i686
AddonCompatCheckDisabled: False
ApportVersion: 2.14.1-0ubuntu3
Architecture: i386
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: ubuntu 2391 F.... pulseaudio
BuildID: 20140428194004
CasperVersion: 1.340
Channel: Unavailable
Date: Sat May 31 16:40:42 2014
Extensions: extensions.sqlite corrupt or missing
ForcedLayersAccel: False
IfupdownConfig:
 # interfaces(5) file used by ifup(8) and ifdown(8)
 auto lo
 iface lo inet loopback
IncompatibleExtensions: Unavailable (corrupt or non-existant compatibility.ini or extensions.sqlite)
IpRoute:
 default via 10.0.2.2 dev eth0 proto static
 10.0.2.0/24 dev eth0 proto kernel scope link src 10.0.2.15 metric 1
IwConfig:
 lo no wireless extensions.

 eth0 no wireless extensions.
LiveMediaBuild: Ubuntu 14.04 LTS "Trusty Tahr" - Release i386 (20140417)
Locales: extensions.sqlite corrupt or missing
Plugins:
 iTunes Application Detector - /usr/lib/mozilla/plugins/librhythmbox-itms-detection-plugin.so (rhythmbox-mozilla)
 VLC Multimedia Plugin (compatible Videos 3.10.1) - /usr/lib/mozilla/plugins/libtotem-cone-plugin.so (totem-mozilla)
 Windows Media Player Plug-in 10 (compatible; Videos) - /usr/lib/mozilla/plugins/libtotem-gmp-plugin.so (totem-mozilla)
 DivX® Web Player - /usr/lib/mozilla/plugins/libtotem-mully-plugin.so (totem-mozilla)
 QuickTime Plug-in 7.6.6 - /usr/lib/mozilla/plugins/libtotem-narrowspace-plugin.so (totem-mozilla)
PrefSources: prefs.js
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
Profiles: Profile0 (Default) - LastVersion=29.0/20140428194004
PulseList:
 Error: command ['pacmd', 'list'] failed with exit code 1: Home directory not accessible: Permission denied
 No PulseAudio daemon running, or not running as session daemon.
RelatedPackageVersions:
 rhythmbox-mozilla 3.0.2-0ubuntu1
 totem-mozilla 3.10.1-1ubuntu4
RfKill:

RunningIncompatibleAddons: False
SourcePackage: firefox
Themes: extensions.sqlite corrupt or missing
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 12/01/2006
dmi.bios.vendor: innotek GmbH
dmi.bios.version: VirtualBox
dmi.board.name: VirtualBox
dmi.board.vendor: Oracle Corporation
dmi.board.version: 1.2
dmi.chassis.type: 1
dmi.chassis.vendor: Oracle Corporation
dmi.modalias: dmi:bvninnotekGmbH:bvrVirtualBox:bd12/01/2006:svninnotekGmbH:pnVirtualBox:pvr1.2:rvnOracleCorporation:rnVirtualBox:rvr1.2:cvnOracleCorporation:ct1:cvr:
dmi.product.name: VirtualBox
dmi.product.version: 1.2
dmi.sys.vendor: innotek GmbH