After installing, create .foprc in your home dir with the following

FOP_OPTS="-Xmx###m"
FOP_HOME="/opt/fop"

Delete and replace the #'s with the amount of RAM your computer has 
in megabytes.

Use can run "free -m" in the terminal to get the info:
Example :

FOP_OPTS="-Xmx1024m"     // If you have a GB RAM
FOP_HOME="/opt/fop"
