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
usr@srv % kcmshell4 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 ;-)