I think I'm missing a plugin...
For me, it's a bit of a classic WTF (I've took this image about 10-ish years ago), but found it when rummaging through some folders on my HD - It comes from a Mozilla 0.x release, long time before it became the beast that is Firefox...
Can you say "Recursive"?
They actually still have that plugin in Firefox, but they renamed it the "Mozilla Default Plugin" now. Still, it doesn't pop up like that in FX3.
The best bit is that you can actually disable the Mozilla Default Plugin. Not willing to try it right now though....!