New file type icon

Hi,
Suppose I have file type called bla, i.e. the file is name by somefile.bla and I have 16*16 gif image named by bla.gif and this image is placed in \editor\filemanager\browser\default\images\icons .

Now I want the file browser displays the file named somefile.bla iconized by bla.gif. Of course I will set the config to allow uploading of this file. How can I push the file browser to assign the new gif icon to the new extension as decribed above?

Best Regards,
Said Bakr.