i can't install java

[juan]

i've install java on my windows system, the path is correct, java works 
well. But mozilla doesn't. When i watch a java web, it says to download 
the plugin, and i click on it. I have download it many times and it says 
  the instalation was succesful. But it never works, the next time i 
enter to the web (any java web) it says again to download de pluin.
How have i to install it?

Juan