Not all Firefox extension will work. Obviously You want to try.
After You unzipped the xpi installer You had: folders with files inside.
The files go into the corresponding K-Meleon folders.
chrome - > chrome.
jar is a chrome file. It goes to ./K-Meleon/chrome.
(jar is another name for zip - peek inside You will need the info later)
outside the folders You have a install.rdf, *.js, and a *.manifest file.
install.rdf makes sure that the XPI installer only installs with applications that the authors want - not used by k-meleon.
install.js the same.
the manifest file is used in K-Meleon chrome - but You must edit its paths so that they fit to the new location.
For an example edit - compare Newsfox Firefox extension with K-meleon extension.
When the manifest is finished?
You may have to create a *.kmm. Examples that start a XUL application are newsfox.kmm , mtypes.kmm, console2.kmm in folder ./K-Meleon/macros.
JarTester an application that lets You start XUL during tests is at
K-Meleon extension page. It helps You to choose which XUL files inside the jar must be started by the kmm.
During the first tests You should also look into error-console. It sometimes helps You to know if You have an error and what type. Errors that say ... cannot find a file in Firefox/chrome/... are normally show stoppers.