I have just updated my system to use oracle java 8 build 91 (latest and greatest) and can't get the firefox plugin to work. Every time I try to verify it, it crashes.

When I tried the approved methods of installing the firefox plugin using symlinks, firefox didn't even see the darn thing and kept reporting that I was using version 10.55 (from java 7) which is GONE. When I copied libnbjp2.so into the firefox plugins directory, it at least saw it and removed the reference to the old one, which I noticed had parked itself in pluginreg.dat and could not be deleted in any other way. I also copied this new lib to /usr/lib/mozilla/plugins (why does this exist?) and ~/.mozilla/plugins and it didn't help.

Anyone know what gives? Can this combination of things be gotten to work at all, and how do I troubleshoot the problem?

Seems to me there might be a bug here as the plugin manager gave different results for the same file depending on whether it was a link or a copy. And of course, the java plugin still doesn't work...

To be really, really clear there is now only one Java installation on this machine:

java version "1.8.0_91"

Java(TM) SE Runtime Environment (build 1.8.0_91-b14)

Java HotSpot(TM) 64-Bit Server VM (build 25.91-b14, mixed mode)


2 Answers 2


I use the same versions.

ricard@cruz-xxxxxx:~/.mozilla/plugins$ ls -liah

12583228 lrwxrwxrwx 1 ricard ricard   43 jun 27 10:43 libnpjp2.so -> /usr/java/jre1.8.0_91/lib/amd64/libnpjp2.so

ricard@cruz-xxxxxx:~/.mozilla/plugins$ java -version
java version "1.8.0_91"
Java(TM) SE Runtime Environment (build 1.8.0_91-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.91-b14, mixed mode)

ricard@cruz-xxxxxx:~/.mozilla/plugins$ /usr/bin/firefox -version
Mozilla Firefox 47.0

Do you have another java plugin activated in firefox add-ons?

If not, try to do this steps again:

  1. Install/Update new java (omit in your case)
  2. Close firefox sesion
  3. Remove old symbolic link and create a new one with the path to your latest jdk or jre
  4. Delete pluginreg.dat ~/.mozilla/firefox/XXX.default) and restart firefox.


  • The issue here was apparently pluginreg.dat stubbornly insisting that an old version of the plugin was installed, even when it wasn't. You can fix it the long way round, like I did, or simply delete it and restart firefox which evidently rebuilds it as Ricard has suggested.
    – MrChuck
    Jun 28, 2016 at 12:42

It seems I inadvertently solved my own problem by making a hard copy of the plugin--which deleted the reference to the old one in pluginreg.dat. On an impulse, I went back and deleted the copy and reinstated the symlink and voila it now works.

This is all voodoo as far as I'm concerned and I still think there's a bug in how firefox is detecting and doing things with this plugin. However it's now gone away so I guess it's just something to be mindful of--pluginreg.dat is stubborn and may not let go of old things easily.

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