How to configure the preferred application?
 

I want to set up the preferred application at will, say, browsing with firefox instead of Konqueror. I go to the preferences but firefox isn't in the list and it requires command when choosing custom web browser. What should be done here?

Thanks

You should be able to supply firefox-bin as the custom application.

But how? There is only a fill-in blank no options.

You could try using KDE button>Preferences>File Browsing>File Association
then select text and then HTML to change the default application. You can either browse to your preffered application or use the command line command.
I'm telling you all this with reference to RedHat Linux and KDE in mind, you should have a similar tool in your distro. Let me know if it helped.