Mozilla requires a license statement and provides a clearly defined set of
options
I was not aware of that. I thought the license name was a free text field.
That may mean the two small scripts (in the attached archive) I wrote some
time ago may be modified to automatically list the add-ons whose authors
choose one of the seven default licenses. I guess most of the free software
add-ons must be under one of those seven licenses. More add-ons (e.g.,
"HTTPS Everywhere" under the "Multiple" license, what is basically
meaningless to decide the free/proprietary status) could then be added
'pop-addons' aims to download Web pages of add-ons from addons.mozilla.org.
'free-addons' takes in argument the directory created by the previous script
(or even nothing if the directory is not renamed and the script is called
from the parent directory) and classify the add-ons w.r.t. their licenses,
either asking or automatically, if it has already got the answer (during the
same execution, a previous execution or even during the execution of another
user who would have shared her accept/reject files). Writing down the seven
licenses in the accept file and slightly modifying the script to
automatically reject any other license is easy.