Firefox plugins

I successfully installed 2 extensions (for PDF files and IDND) on my
laptop running Mandriva 2005LE but the same 2 extensions won't work on my
desktop running Mandriva 2005LE. When I look at the extensions on the
desktop (Tools->Extensions), the extensions are listed but it gives the
message that the extensions will be installed after a browser restart.
Well, I closed all running instances of firefox (version 1.0.7) but the 
extensions still don't work after restarting firefox. I get the same
message about restarting the browser to install the extensions. Any ideas?
I suppose I could restart the X server and, if that don't work, restart
the PC.