I have the same problem as Nemros. Even though I did a "yum install @kde-desktop", I have created a separate user for KDE and never logged into it as my "Gnome user".
The problem is definitely not in /home - I've tried renaming .kde, creating a new profile for Firefox and fiddled with various other things in the Gnome user's /home directory.
With mozplugger, okular is used instead of evince to open .pdf files in Firefox and, as stated above, "Open Containing Folder" opens the download directory with Konqueror, not Nautilus.
system-config-services also presents me with a KDE prompt when I use it. There may be other instances too, but these are the main ones I've noticed.
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