Running Java plugin 1.5 on Firefox + Snow Leopard

Question

I have a Java applet that needs to be able to run on Java 1.5.

I have successfully installed Java 1.5 on Snow Leopard and I am able to use it to run applets in Safari by changing the order of the versions in Java Preferences.

However, Firefox (3.5.9) doesn't seem to be able to pick up the changes and keeps reverting to using the Java 1.6 plugin.

How do I force Firefox to use the Java 1.5 plugin?

I tried re-linking the /System/Library/Frameworks/JavaVM.framework/Versions/CurrentJDK folder to point to my 1.5 directory, but that seems to change the system-level Java runtime, not the Firefox plugin (it opened up the console differently, but inside the console it reported Java plugin 1.6.0).