Firefox uses not fully functional Kghostview to open PDF's in KDE instead of the system default KPDF

When opening a PDF in firefox in KDE, it uses Kghostview as a default application, but in Kghostview the little overview pictures of pages don't work. The KDE itself opens PDF's with KPDF that works very well. I propose to raise priority of KPDF mailcap entry so Firefox would also use KPDF by default, so we would have a fully working application for opening PDF's.