The default applications chooser (kcmshell5 componentchooser) queries available web browsers by looking for
'WebBrowser' in Categories and ('x-scheme-handler/http' in ServiceTypes or 'x-scheme-handler/https' in ServiceTypes)
in CfgBrowser::load(KConfig *) in plasma-desktop/kcms/componentchooser/componentchooserbrowser.cpp
This change sets the MimeType in Konqueror's desktop file so that it will be recognised by that query.