[Karmic] apturl does not work out-of-the-box
Binary package hint: ubufox
In Karmic's Firefox (K/X/Ubuntu 9.10), the apturl links don't work out-of-the-box.
Very boring for beginners, as the community wiki (English and French, I don't know for others) use plenty of APTURL links, and so does the new Getdeb website.
I remember it was working out-of-the-box with Ubuntu 8.04 and 9.04.