When reviewing packages from mentors.debian.net I like to have them under version control so I can easily compare different versions, write patches and clean up autogenerated files. So when looking at a package I do a
git-import-dsc --download http://mentors.debian.net/debian/pool/main/x/xul-ext-firetray/xul-ext-firetray_0.2.8-1.dsc
This command first fetches the files via dget from devscripts and then imports the upstream sources onto the upstream branch (upstream by default) and the debian modifications onto the debian branch (master by default). I can then invoke git-buildpackage as usual. Since this works incrementally I can import newer versions into the same repository and use git diff to see the changes.
If I'd like to hack on a random Debian package (say xul-ext-nostalgy) I usually use:
git-import-dsc --download xul-ext-nostalgy
This uses apt-get source to fetch the source package and imports it into git using the same branch layout as described above so I can use all the familiar git commands to generate patches, etc..
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