If you goto about:plugin , and Java Plug-in is not there. ( NOTE : you can also see Java Plug-in from Add-ons > Plugins ) You can install it manually using the following instructions below. 1. Copy NP*.dll from C:\Program Files\Java\j2re1.4.2_19\bin to C:\Program Files\Mozilla Firefox\plugins 2. restart firefox That's it. ref : mozillazine