Firefox: pluginreg.dat - What Dat?

The mise en scène:

  1. Oracle discovers a security issue with Java 1.7.0_07. 
  2. Oracle patches same and releases Java 1.7.0_10. 
  3. Firefox blacklists 1.7.0_07. 
  4. Java apps that used to work now don't.  
OK so far so good. So we upgrade to latest Java on computer A (Fedora 17 x86_64) and now things "just work". And "about:plugins" lists the new plugin as 1.7.0_10 as does

So far so good.

Now update computer B (again Fedora 17 x86_64) and while the upgrade seems to take, java apps are not working, "about:plugins" lists the plugin as 1.7.0_07 as does

Even more strange - on computer B - go to about:config and set plugin.expose_full_path to TRUE and (I wish I had a screenshot of this but trust me it happened) the plugin is listed as 1.7.0_07 at the same time as the path is listed as /usr/java/jdk1.7.0_10/jre/lib/amd64/

Clearly something was amiss. And indeed it was. It was the pluginreg.dat file. Mine was located at


Deleting this file, forcing a rebuild by again going to about:plugins fixes the issue. Java apps now work, about:plugins output is sane and the plugincheck website is as well.  

Prior to deleting it (or renaming) you could see that the file indeed had out of date or out of sync info.

 grep '1.7.0_07' BACKEDUP_pluginreg.dat 
     Java(TM) Plug-in 1.7.0_07:$
     33:application/x-java-applet;jpi-version=1.7.0_07:Java&#153 Plug-in::$
     34:application/x-java-bean;jpi-version=1.7.0_07:Java&#153 Plug-in::$

It turns out that another file in the same directory, addons.sqlite can also lead to similar problems and can require deleting also, although it was not needed in my case.

When upgrading Java this can come in handy as well. 
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