BPIP website is clearly NOT the same thing as BPIP extension.
I'm obviously talking about the extension and not the website.
Even if you can download and edit .xpi files, there are different licenses with all rights reserved, so you can't edit them just like that.
.xpi files are Firefox extension files. When you install the BPIP extension, its data is stored in a .xpi file on your computer. We aren't downloading and editing anything, but rather opening the extension's source code to examine it.