Where files are unpacked if installed globally?

Hi,

I have an extension (signed), which is supposed to be unpacked.

If I drag n drop my xpi on the Firefox addon page, my extension is installed correctly, all files are unpacked in my extension directory under my profile, and extension is working fine.

If choose to install it by dropping the {app_id}.xpi file inside %appdada%\Mozilla\Extensions\{ec8030f7-c20a-464f-9b0e-13a3a9e97384}\
Then I open Firefox, it prompts me to accept the install, what I do.
On the addon page my app seems to be active and installed.
I open my extension folder under my profile : Mozilla\Firefox\Profiles\kgbrptal.default\extensions\{app_id}
but it contains only 1 empty folder (named ‘content’ which is part of my extension). Therefore my extension is not working.

update
Seems like the empty folder content/ I found has nothing to do with unpack property. If I don’t use unpack it is still created. I think it is because I am doing var file = FileUtils.getFile("ProfD", ["extensions", extension_id, "content", "config.js"]);

my question now is :

With option <em:unpack>true</em:unpack>, where are the unpacked files if I install the add-on globally? (inside %appdada%\Mozilla\Extensions\{ec8030f7-c20a-464f-9b0e-13a3a9e97384}\)
How can I read them using FileUtils.getFile ?