TWO:kfm browser register the application
1) Edit->application (or global application)
|Enter the name you wish to call this (doom eg)
|Click on the Execute tab
Enter the location of the execute command
(often, simply the name, rather than the full path is sufficient
Change your icon (if you want) as per the same instructions for the mime type.
|Click on the Application tab.
Where it says "Name (in your language)" it is essential that you enter something unique here. It is essential that you enter something.
2) Scroll down the list of mime-types until you find the application/doom that you entered in the above STEP ONE
Select it by shifting it in with the <- arrow.
Click OK, you're done.