Annoyingly, KDE’s PDF viewer okluar always opened links to websites with an editor presenting me the source code. But I just figured out how to change this behavior.

KDE maintains a central config defining what to do with certain file types. Unfortunately, in my case the default application for HTML files was an editor (kwrite/kate). I don’t know who or what defined this stupid behavior, but there is a tool called kcmshell4 to edit the KDE configuration. That said, to edit the filetype-application-mapping hand it the parameter filetypes :

You’ll get a dialog to define a mapping for each known file type. In my case I had to configure okular to open links to HTML pages with konqueror. Hope that helps you to save some time ;-)