Firefox dont want to install new extensions - Why?

Hello,

I use Firefox 1.5 (French version, but I have the same problem in
then English only version, that I installed temporary) on a Windows XP
machine.

I have the message: "Software installation inactive. Click on Options
Modification button and retry" =3D=3D> It did not work; event when you
change all the choices in Options/Content (Options/Contenu in French).

By the way, the option/Web functionality don't exist, nor in the French
nor in English versions.

Why extension installations are not functioning?

Thank you,

Roger Gari=E9py