The following might work:
Download the rpm file jre-7u21
. Then, on this rpm file (jre-7u21-linux-i586.rpm), run the following as root:
Then you will have a Vector package. After uninstalling any previous jre that you have, install the jre-7u21-linux-i586.tgz package (right-clicking on it in Thunar should give you this option). Then, as described here
, create a link:
ln -s /usr/java/jre1.7.0_21/lib/i386/libnpjp2.so
After that, restart firefox, and check under Tools/Add-Ons to make sure it has been installed.