How to retain native application icons?

[N. W.]

Dear Lubuntu Artwork developer(s),

what if someone wants to use the Box icon theme, but at the same time
wants all applications to use their native application icons?

With native application icons I mean: Firefox for example has it's own
native icon, but it is overwritten by the Box icon theme Firefox icon.

What's the best approach to do that?

Would it be deleting the "/usr/share/icons/lubuntu/apps" folder?

Or how should it be done? Or is there a setting to toggle this?

And something else:

I just tried something with Lubuntu 14.04 LTS "Trusty Tahr" inside a
virtual machine:

I deleted the entire "/usr/share/icons" folder.

This is what I noticed after doing that:

First of all: When browsing in PCManFM, there still was a folder icon
showing up.

It was a yellow folder icon which looked very similar to the folder
icon that is being used in Microsoft Windows 7:

http://www.sevenforums.com/geek/gars/images/4/7/types/thumb_Yellow_Folder.png

Where does it come from? I mean, I deleted the entire
"/usr/share/icons" folder...

I also noticed that, even though I had deleted the entire
"/usr/share/icons" folder, Firefox still had it's native application
icon available. As well as Sylpheed and some others. I assume this is
normal because they come with their own icon "built-in"?

However, Audacious for examle did not have an application icon
available. Why not?

Regards