Comment 10 for bug 98725

root@xx:~ # update-alternatives --config java

There are 4 alternatives which provide `java'.

  Selection Alternative
-----------------------------------------------
          1 /usr/lib/jvm/java-1.5.0-sun/jre/bin/java
          2 /usr/bin/gij-wrapper-4.1
*+ 3 /usr/lib/jvm/java-gcj/jre/bin/java
          4 /usr/lib/jvm/java-6-sun/jre/bin/java

Press enter to keep the default[*], or type selection number: 4
Using `/usr/lib/jvm/java-6-sun/jre/bin/java' to provide `java'.

Restart of liferea, same issue:
/usr/bin/liferea-bin: symbol lookup error: /usr/lib/jvm/java-1.5.0-sun-1.5.0.11/jre/plugin/i386/ns7/libjavaplugin_oji.so: undefined symbol: PR_NewMonitor

Now, if I restart firefox:
/usr/bin/liferea-bin: symbol lookup error: /usr/lib/jvm/java-6-sun-1.6.0.00/jre/plugin/i386/ns7/libjavaplugin_oji.so: undefined symbol: PR_NewMonitor

so it may be a problem with firefox...
I have firefox 2.0.0.3+1-0ubuntu1.