Firefox 15 and Java 7, applets won't load

Hey, people, the name pretty much says it all. I'm on Firefox's beta channel so I'm running Firefox 15 (x32)
This information from the Java console (which I've noted other people have problems with but comes up for me just fine) will tell you what versions the bits are of Java:
Java Plug-in 10.5.1.255
Using JRE version 1.7.0_05-b06 Java HotSpot(TM) Client VM
From the link in the Control Panel: Java Standard Edition Version 7 Update 5 (x32)

Everything about the version of Java I have installed works except the actual function of the script on web pages. When I try the test on the Java website, I get "ClassNotFoundException" when I click for details. Any ideas as to why? My dad suggested downgrading Firefox back to 14 so I might try that if I can't get it to work in 15.

Thanks!

It says it up to date, and the plugin is enabled.

I just got a new laptop with Windows 7 Pro 64-bit. I installed Firefox 15 to get online.
I noticed that online Java applets didn't load. The version of Java that came with it
was 6.xx and was already disabled because it was a security threat. I updated to Java 7 U7.

The online applets then worked correctly for about a day
then again stopped loading. Java is enabled and up to date but nothing I try seems to
fix the problem. I keep getting a ClassNotFound Exception error.

I tried system restore but, as with every computer I've ever owned, it
didn't work, saying some unspecified file could not be accessed so the restore failed.

So I tried IE but the online Java apps don't load there either.

Does anyone have a clue on how to solve this most frustrating problem? TIA

I tried what A Guy mentioned in his last note. I found the one dll, npoji610.dll, but the other, npjpi160.dll, wasn't there. I did find a npjpi170_07.dll though.

So I copied and pasted them both to Program Files (x86)/Mozilla Firefox/search plugins, which was the closest I could find to what the article mentioned.

But it was all moot since the problem remains.

Any other ideas?

Hey, that seemed to work. :) The sites I visit with apps all load now after I did what you suggested. I'm using the Java 1.6. If things start to go crazy again I'll try the 1.7 version but for now :). Thanks Slartybart.

I uninstalled both FF and Java. Plus I went into the registry and deleted anything with Firefox or Mozilla in it, as well as anything with Java mentioned.