MIME and metadata stuff

[Bruce Stephens <bruce cenderis demon co uk>]

I'm sure I used to be able to drag a link from Netscape Navigator to
the desktop, and get a usable link there (courtesy of gmc).  

That doesn't work any more: I get an icon with a random name
(beginning with "url", so it *knows*), and the file contains the right
URL.  Double clicking on such icons doesn't visit that URL.

So, presumably there's some set up that's not present on my machine.
How do I fix it?  Alternatively, where do I read about all this stuff,
so I can work out for myself what's wrong?