xpath expressions fail to properly deal with some namespace variants

we should do the whole namespace business proper. full spec is http://www.w3.org/TR/xpath ... also xpath tool is buggy, so only some variants of doing this will work.

This bug was fixed in the package mozilla-devscripts - 0.19

---------------
mozilla-devscripts (0.19) unstable; urgency=low

  * xpi.mk:
    - get rid of temp directory; extract xpi file directly into installation
      directory
      - update src/xpi.mk
    - correct permissions of installed files and add
      MOZ_XPI_PRESERVE_PERMISSIONS to disable this behaviour (Closes: #556741)
      - update src/xpi.mk
    - drop support for deprecated MOZ_EXT_NAME and MOZ_XPI_MOZILLA_DIRS variable
      - update src/xpi.mk
    - add new MOZ_XPI_INSTALL_DIRECTORY variable
      - update src/xpi.mk
  * med-xpi-{pack,unpack}:
    - Drop med- prefix.
      - rename man/med-xpi-{pack,unpack}.1 to man/xpi-{pack,unpack}.1
      - rename src/med-xpi-{pack,unpack} to src/xpi-{pack,unpack}
      - update README
      - update src/Makefile
      - update src/xpi.mk
  * xpi-data:
    - Add Firefox 3.6 and Thunderbird 3.0 for lucid.
      - update src/xpi-data-Ubuntu.mk
    - Convert xpi-data-*.mk files into xul-app-data.csv* files for dh_xul-ext
      - remove src/xpi-config.mk.in
      - remove src/xpi-data-Debian.mk
      - remove src/xpi-data-Ubuntu.mk
      - remove src/xpi-data-all.mk
      - remove src/xpi-data-common.mk
      - add src/xul-app-data.csv.Debian
      - add src/xul-app-data.csv.Ubuntu
      - update src/Makefile
  * dh_xul-ext:
    - Split substvars calculation from xpi.mk into new dh_xul-ext.
      - add src/dh_xul-ext
      - update src/Makefile
      - update src/xpi.mk
    - Move compare_versions from moz-version into separate module moz_version.py
      - add src/moz_version.py
      - update src/moz-version
      - update src/dh_xul-ext
    - Install moz_version.py using python-support
      - update debian/control
      - update debian/rules
      - update src/Makefile
    - Add "xul-ext" dh sequence
      - add src/xul-ext.pm
      - update src/Makefile
      - update debian/control
    - wrote man page for dh_xul-ext
      - add man/dh_xul-ext.1
      - update src/Makefile
  * install-xpi:
    - Split xpi installation from xpi.mk into new install-xpi script.
      - add src/install-xpi
      - update src/Makefile
      - update src/xpi.mk
      - update debian/control
    - wrote man page for install-xpi
      - add man/install-xpi.1
      - update src/Makefile
    - add --install-dir parameter to install-xpi
      - update man/install-xpi.1
      - update src/install-xpi
    - create links for architecture independent extensions in /usr/share instead
      of /usr/lib (Closes: #564671)
      - update src/install-xpi
    - create additional symlinks for icedove and thunderbird, because they do
      not scan /usr/{lib,share}/mozilla/extensions/$target_application
      - update src/install-xpi
  * moz-version:
    - Add parameter for converting Mozilla versions into Debian upstream
      versions and the other way round.
      - update man/moz-version.1
      - update src/moz_version.py
      - update src/moz-version
    - Add a test suite for testing moz-version --compare
      - add tests/test-moz-version
      - update debian/rules
      - update src/Makefile
  * packaging:
    - add homepage field
      - update debian/control
...