$ mkdir fennec && mv <upstream_tarball>.tar.bz2 fennec/fennec-source.tar.bz2
$ tar -czf fennec_<version>.orig.tar.gz fennec
$ wget http://repository.maemo.org/extras-devel/pool/fremantle/free/source/f/fennec/fennec_7.0.1-2.diff.gz -O fennec/fennec.diff.gz
$ cd fennec && gunzip -c fennec.diff.gz | patch -p1 && rm -f fennec.diff.gz
$ sed 's/7.0.1-2/<VERSION>/' -i fennec/debian/changelog
$ cd fennec && dpkg-buildpackage -S -sa -rfakeroot -us -uc