Comment 3 for bug 155505

I had this problem too. It apparently occurs if you have the MOZILLA_FIVE_HOME environment variable set (some apps need this, ex. those that use the Java SWT browser widget). The kompozer startup script looks for a run-mozilla.sh script in the directory specified by MOZILLA_FIVE_HOME if it is set. I guess for firefox 3 it's no longer there.

The workaround is to unset MOZILLA_FIVE_HOME before running kompozer, or to alter the /usr/bin/kompozer script and add a export MOZILLA_FIVE_HOME="" to the start of it.