Firefox does not open .PNG files anymore

[Marcelo Magno T. Sales]

Hi,

Since recently, possibly after the upgrade to 3.0.6, Firefox does not 
open .PNG files anymore. When I click a link which points to a .PNG 
file, Firefox asks for an external application to open the file instead 
of opening it directly in Firefox. How do I get the old behavior back?

Thanks,

Marcelo