If you use Jdem.cz then use Ubiquity with Jdem command. Why? Because it's the easiest way to use Jdem.cz.
If you use Firefox browser with Ubiquity extension than click Subscribe in the upper-right corner and confirm the next dialog. Now you can use Ubiquity command jdem. Just press CTRL+space and write jdem.
Learn more about Ubiquity (or in Czech).
Made by Martin Hassman.