I have no answer to your question. Just wanted to point out that the last code submit for KompoZer was dated September 2011.
Given Firefox made significant changes to its own code during that period, some breaking backward compatibility, I hope you have the software skills to perform the “code-patching” work that will be required to ensure compatibility with current versions of the browser.
The only alternative, also fraught with roadblocks, is trying to slim down an old 2011 version of Firefox source-code, such that it is limited to performing the WYSIWYG functionality.