In K=Meleon 74.0 not 74.7+1, The only Firefox CacheViewer Extension that works is CacheViewer Fx21
https://addons.cdn.mozilla.net/user-media/addons/319027/cacheviewer_fx6-1.0-fx-windows.xpi which has to be renamed to {81328583-3CA7-4809-B4BA-570A85818FBB}.xpi.
Also The CacheViewer macro from
http://kmext.sourceforge.net/km74/cacheviewer-km74.7z at K-Meleon Extensions Central is needed to make it work.
Both Firefox Extensions CacheViewer
https://addons.cdn.mozilla.net/user-media/addons/2489/cacheviewer-0.8.2-fx.xpi and CacheViewer2 cacheviewer2-1.6-fx.xpi Do not work with K-Meleon 74.0
Eventhough cacheviewer2-1.6-fx.xpi does work with K-Meleon 74.7+1