Although most browsers are happy to allow both signed and unsigned Java applets to queue print jobs, this behaviour is explicitly blocked by the standard settings in Opera.  Although there is an argument to be made in terms of security for this, modern Java applets run in a sandbox, which means they are relatively safe to use, and Opera is the only popular browser to prevent Java applets printing by default.  As Java will also ask the user if they wish permit printing (sometimes several times, depending on how the applet is coded), it can be desirable to override this feature of Opera.  However, there is no obvious way to do this through the browser itself.

Start by making sure that you have closed any Opera browser windows you may already have open.  You will now need to manually open and edit the "Opera.policy" file - obviously, any alterations you make to this file are made at your risk.  On a standard Windows installation, the file can be found in: c:program filesoperaclassesopera.policy.  Before editing this file, ensure you have make a backup copy - this means that if you edit the wrong part of the file, or enter information incorrectly, you can go back to a working copy of the file.

Open the file in a text editor such as Notepad, and find the line that says: grant {.  Just underneath, add the following text:

permission java.lang.RuntimePermission "queuePrintJob";

Now close the file, and re-start Opera.  Any Java applet that needs to print material to the printer will now have the privileges to do so.