File associations in Thunar

[Mark]

When I install or upgrade software on my system, the association between file 
types and the applications used to open them often changes, sometimes with 
bizarre results.  As a recent example, double-clicking on a .gif file 
resulted in an attempt to open it in Internet Explorer -- before this, I 
wasn't even aware that I *had* an IE clone as part of Wine.  Images tend to 
be the most prone to changes, typically fluctuating between GIMP, Ristretto, 
and ShowFoto.

How are these associations determined?  Is there some central location where I 
can see what's associated with what?  Is there any way to prevent these 
changes?

Thanks,
Mark