I finally got tired of mozless not working on my Ubuntu 10.04 system.
Brief instructions and how I fixed it:
Download the xpi, unzip and create a file called chrome.manifest in the root of the extension. Fill it with the following:
content mozless chrome/content/
skin mozless classic/1.0 chrome/skin/
locale mozless en-US chrome/locale/en-US/
overlay chrome://browser/content/browser.xul chrome://mozless/content/mozless.xul
overlay chrome://browser/content/navigator.xul chrome://mozless/content/mozless-mozilla.xul
overlay chrome://mozless/content/mozless.js
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Then in the chrome directory, unzip the mozless.jar file and delete the file itself.
zip up the directory and install your 'new' extension, and delight at 'j' and 'k'.