Some time we need source rpm to build custom rpm. You can download source rpm via yum in fedora.
To download source rpm of firefox in tmp folder.
cd /tmp yum install yum-utils -y yumdownloader --enablerepo=rpmfusion-free-rawhide --source firefox
To check the downloaded rpm run
lsfirefox-3.6.4-1.fc13.src.rpm
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