Thanks again, but... it's not what I mean.
Before my file system repair, when I chose the Root folder tab of the navigation panel, I could see the file system tree (as this Root folder has the URL "/") and then I could go down in the FS heirarchy.
I can't any more, because there is no FS tree displayed in the panel area -- which is as large as before.
This is what I'm trying to recover and can't find anything related looking at the Konqueror configuration files in my $HOME.
I suspect the configuration is somewhere else, because the same behaviour comes when I lauch Konqueror with the root account, for instance. Do you know where I should look?
Among the files in the lost+found, I found an XML file with this open tag:
<kpartplugin name="FSViewPart" library="libfsviewpart" version = "1">
Would it be related to my problem? Where is this file located?