Important:
* Port to gecko 1.9/XULrunner. Maybe look at mozilla's reftest helper (mozilla/layout/tools/reftest/) ?

Improvements:
* Test on a big endian machine
* Improve thumbnail creation time
* Thumbnailing service? I.e. background process (which exits after some time without requests),
  which the frontend tells which files/pages to thumbnail.
* Find out why it crashes on https:// sites, and on http://slashdot.org/, if I disable the profile
* Fix the output on framed pages
* Use <canvas> and drawWindow() instead of the low-level stuff (<canvas> can operate without a document,
  so we don't need to put it in an embed)
* Add memory size and CPU time limit (look at totem-video-thumbnailer/indexer)
* Implement printing to printer, using the gtk 2.10 print APIs
