File association, download eventlistener (?)

[Kjell]

Hi all

I am new to extension development, but as being a passionated javascript guy
i could quickly get something started.. My question is, how can i make my
extension look out for a specific file to be downloaded?

I want to make an extension that does something if a specific file extension
(i.e. *,jpg) has been successfully downloaded. (associate my extension as
default filetype handler.)

if(downloadFinished && filetype == myEXT)
{
doSomething( file ); // could popup a sidebar, providing options for the
file, etc..
}

Any help is much appreciated.
TIA