See:

• http://kb.mozillazine.org/Java

• http://kb.mozillazine.org/Determining_plugin_directory_on_Linux
• https://developer.mozilla.org/en/Gecko_Plugin_API_Reference/Plug-in_Basics#How_Gecko_finds_plug-ins

Like I said, I have been to that page and followed the instructions, but there is still no java plugin in my add-on manager. The correct symbolic link is in my /usr/lib/mozilla/plugins directory, but it does nothing.

Another thing I tried was to find the "real" plugin directory in my OS according to this page. The libnullplugin.so file was not in any of the mozilla directories, but was in a directory for another application entirely--matlab, the computer algebra system, of all things. I copied the libnullplugin.so file to my /usr/lib/mozilla/plugins directory and my ~/.mozilla/plugins directory. I re-started firefox and still no java plugin.

Thanks Anyway--I'm still trying

You can check out the installation path of the other plugins on the about:plugins page.

I have plugins in these locations:

/usr/lib/mozilla/plugins/
/usr/lib/browser-plugins/
/usr/java/jre1.7.0_45/lib/i386/libnpjp2.so

A possibility is to create a ~/.mozilla/plugins/ directory and place a symlink to the libnpjp2.so Java plugin file in that folder to see if it helps.

Just to be sure, since your Firefox appears to be 32-bit, the Java plugin should be 32-bit also.

Ugh!

Like an idiot I tried to copy a file to a directory that didn't exist--there was no error because the name of the file was just changed to the would-be directory name--plugins.

Well, thanks for your advice, actually making that directory did the trick!

Andrew