This is a Frequently Asked Question, but I haven't found a solution to my problem yet. Or maybe I just didn't recognize it when I saw it.

I searched the forum, read the Firefox Help site, but nothing seems to help.

I have installed Mozilla 1.4 on my system (Mandrake 9.2.), but now I am trying to get Firefox 9.1. to work

I tried it the easy way by copying the plugins in the Mozilla Plugins Folder to the Firefox Plugins Folder but that doesn't seem to work.
I copied the following plugins from Mozilla to Firefox : flashplayer.xpt libjavaplugin_oji.so libnullplugin.so nppdf.so

For the java-applet issuing the command
from the Firefox Plugins Folder gives the result : "File already exists"

Where do i go from here ?

There should also be a libflashplayer.so, which is the actual plugin. You might want to download a newer version anyway, as there was one released quite recently.