[Hampshire] Mozilla Firefox plugins directory

I am following instructions* which require me to cd to <quote> Mozilla Firefox
plugins directory </quote>, but I cannot find the directory in order to
change to it. It may well in fact be an Iceweasel directory since I am
running Etch, but I can't find that either.

I have googled repeatedly and found numerous alternative instructions for what
I am trying to do (which all boil down to the same thing anyway), but they
_all_ require me to cd first to my Mozilla Firefox plugins directory.

Could any kind soul give me a suggestion as to what the path to my "Mozilla
Firefox plugins directory" might be so that I can cd to it?

TIA
Lisi

* I am trying to install the Java plugin for Iceweasel. I would be equally
happy to install a Java plugin on Konqueror, Opera or any other reasonable
browser. I have already installed JRE, I just need to sort out my symbolic
links so that I can actually use it in a browser.