Firefox does not open .PNG files anymore

[Bruno Wolff III]

On Sat, Feb 14, 2009 at 09:20:45 -0800,
  Konstantin Svist <fry.kun at gmail.com> wrote:
> 
> The reason why this works the way it does is that when you click the
> URL, the browser doesn't yet know what the target file type is. If the
> file was called "8y2kjndjpwuer", there's no educated guess you could
> make - all you have to go by are the server headers. If it's called
> "foobar.png" it could make a GUESS, but that would be the wrong way of
> doing things (that's what IE does, and I'm sure at least some of its
> vulnerabilities were caused by this behavior in the past).

IE at one time (and may still) did worse than guess, it ignored the content
type headers in some cases. So that if you wanted to say display the
source code of a web page use a file name ending in .html and use a content
type of text/plain, IE would display the page as if it was html rather
than showing you the source listing as intended.