build-dep is not working properly and giving error

I am getting following error when I do build-dep
Presario-CQ42-Notebook-PC:~$ sudo apt-get build-dep firefox
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: You must put some 'source' URIs in your sources.list

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: apt 0.8.16~exp12ubuntu10
ProcVersionSignature: Ubuntu 3.2.0-24.37-generic-pae 3.2.14
Uname: Linux 3.2.0-24-generic-pae i686
ApportVersion: 2.0.1-0ubuntu7
Architecture: i386
Date: Sun May 6 12:04:11 2012
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release i386 (20120423)
ProcEnviron:
 LANGUAGE=en_US:en
 TERM=xterm
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: apt
UpgradeStatus: No upgrade log present (probably fresh install)