no machine with general access to the internet should have such an outdated version of the java plugin installed - it is a security disaster waiting to happen. the exploits for old java versions are pretty wide-spread and it doesn't take any user interaction to get infected...

if you need it for a special application i'd recommend using a portable version of firefox just for this purpose with the plugin enabled, but to keep it disabled in your regular browser instances.

Thank you for your answer. my problem here, is i can not add this java version to firox to enable it !

maybe see if http://kb.mozillazine.org/Java#Windows_installation_issues contains a solution