Hi vze,
Thanks for posting your question here. Since you have already installed Java as you described, I believe you should be able to install the "missing plugin" by clicking the button around or on where you are seeing that message. Generally speaking, if a plugin cannot be installed, you should be be given some additional details which explain why.
If you are unable to successfully install the Java plugin required to use the uploader in this manner, please contact our Customer Support team from under the “Help” tab within your account and we will be happy to continue working with you on this.
-Mike