Are you running IDL 7.0?  If so, there is a known issue with the Firefox xulrunner and there is a patch available from ITT Technical Support.

Thanks. I've followed instructions per Tech Tip 4442, A.2.b, modifying the local path. Still get an error (albeit a different one). I use a network license so A.2.a. is not practical. nathan@iapetus-103> which java /usr/java/jre1.5.0_11/bin/java IDL Version 7.0 (linux x86 m32) IDL> ? idlde.linux.x86: JVM terminated. Exit code=1 /net/cronus/data/opt/local/rsi/idl70/idlde/bin.linux.x86/jre/bin/java -jar /net/cronus/data/opt/local/rsi/idl70/idlde/plugins/org.eclipse.equinox.launcher_1.0.0.v20070606.jar -os linux -ws gtk -arch x86 -launcher /net/cronus/data/opt/local/rsi/idl70/idlde/idlde.linux.x86 -name Idlde.linux.x86 --launcher.library /net/cronus/data/opt/local/rsi/idl70/idlde/plugins/org.eclipse.equinox.launcher.gtk.linux.x86_1.0.0.v20070606/eclipse_1020.so -startup /net/cronus/data/opt/local/rsi/idl70/idlde/plugins/org.eclipse.equinox.launcher_1.0.0.v20070606.jar -exitdata b98012 -application org.eclipse.help.base.helpApplication -data /home/nathan/.idl/itt/idlhelp -topic -vm /net/cronus/data/opt/local/rsi/idl70/idlde/bin.linux.x86/jre/bin/java -vmargs -jar /net/cronus/data/opt/local/rsi/idl70/idlde/plugins/org.eclipse.equinox.launcher_1.0.0.v20070606.jar