Spy der Mann's Journal: How to fix Firefox "can't open containing folder" in Linux

It seems that Firefox doesn't like KDE very much. Now, most Linux users prefer editing files under the command line for fixing this bug. But I come from Windows, so here's how *I* solved it:

Open a new tab on firefox, and type in the url: about:config
rightclick on any of the items, and choose "New - String". When asked "Enter the preference name", type: "network.protocol-handler.app.file". When asked for the value, just type "/usr/bin/konqueror".

Quit Firefox and reopen. Opening folders and files now work!