Can't install XUL package

Hi,

I'm having trouble hand installing a simple XUL application. The app 
works when I access it via a "file:/" URL, but I'd like to access it via 
a chrome URL, i.e "chrome:/leftychord/content/", However, I keep getting 
this message when trying to access it:

"The file /usr/local/mozilla/chrome/packages/core/content cannot be found."

I've also tried variations on this, like appending the name of the xul 
file, but I get the same message. The way I'm trying to install the 
package is:

1.) Create a /usr/local/mozilla/chrome/leftychord directory with 
"content" and "skin" subdirectories. XUL file is in content; graphics 
and CSS are in skin.
2.) Create contents.rdf files for both content and skin directories
3.) editing $MOZILLA/installed-chrome.txt to have "content" and "skin" 
install lines for these packages.
4.) restarting Mozilla.

I also tried creating a JAR file in the chrome directory and altering 
the installed-chrome.txt accordingly. I've gone over the manifest files 
carefully and believe them to be correct. I've not tried the full 
XPInstall method.

So:

What's gone wrong?

Where is it getting "packages/core/content" from?

Is there a debugging technique, or way to observe Mozilla processing the 
installed-chrome.txt file? I want to see where I've confused it.

Thanks