For the XPCOMViewer Firefox Extension to work with K-Meleon 74.0 and K-Meleon 75.0 Beta, download XPCOMViewer
https://addons.cdn.mozilla.net/user-media/addons/7979/xpcomviewer-1.4.2-tb+fx+sm.xpi and rename it to
xpcomviewer@ondrejd.com.xpi
Next copy
xpcomviewer@ondrejd.com.xpi into the extensiosn folder.
Then download XPCOMViewer
http://kmext.sourceforge.net/extensions/xpcomviewer.7z from K-Mwleon Extensions Central
Last extract macros from XPCOMViewer
http://kmext.sourceforge.net/extensions/xpcomviewer.7zinto the K-Meleon Root Folder.