Problem with Firefox "manifest" file

Question

I was trying out this XUL tutorial on Firefox 3.6.13.

The example extension in the tutorial is meant to find files. This is my manifest file:

content findfile file:///home/darthshak/Programs/firefox/findfile/content/
skin findfile classic/1.0 file:///home/darthshak/Programs/firefox/findfile/skin/
locale findfile en-US file:///home/darthshak/Programs/firefox/findfile/locale/

This file is located at /usr/lib/firefox-3.6.13/chrome and is called findfile.manifest.

In /home/darthshak/Programs/firefox/findfile/content/findfile.xul I have put this sample XUL code:

<?xml version="1.0"?>
<?xml-stylesheet href="chrome://global/skin/" type="text/css"?>

<window id="findfile-window" title="Find files" orient="horizontal"
        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">

    <button id="find-button" label="Find"/>
    <button id="cancel-button" label="Cancel"/>
</window>

Now, the darn thing never runs when I execute the following command:

firefox -chrome chrome://findfile/content/findfile.xul

Only a PID is output on the terminal, and nothing appears.

I downloaded the ChromeList extension, and to my chagrin, I found the following directory structure:

findfile/
    content/
        content/
            findfile.xul
        skin/
        locale/
    skin/
        content/
            findfile.xul
        skin/
        locale/
    locale/
        content/
            findfile.xul
        skin/
        locale/

Further, when I launched findfile.xul with the option "Open in new window", nothing appeared. However, it worked only when I chose "Open in new tab" or "Launch".

I tried a lot of things (except, obviously, the right thing which would have solved this problem) which included renaming the .xul file, changing the findfile.manifest file and so on. Oddly, when I added the manifest file in the chrome directory in /home/darthshak/.mozilla/, the manifest did not even register on ChromeList.