Nothing in there looks problematic. All of those settings look redundant to
the defaults Trisquel already sets for Abrowser. I'm not sure where the file
came from though, as it does not look like Trisquel's [package helper][1] for
Abrowser creates it.
If you delete the file with
$ sudo rm /usr/lib/abrowser/distribution/policies.json
then the warning should go away. After that, try reinstalling Abrowser with
$ sudo apt install --reinstall abrowser
to see if the file comes back.
[1]:
https://devel.trisquel.info/trisquel/package-helpers/blob/etiona/helpers/make-firefox
