I think everyone here agrees on that:
* one should use Free software to do its own computing (a search engine on
her website is part of it) unless she does not value her freedom;
* one cannot impose her view on someone's else computing (a search engine on
someone else website is part of it and so is a feature that would filter the
output).
I agree that Trisquel should encourage the participation to the Free software
community. In this way, a company that develop and distribute softwares under
the terms of Free licenses should be preferred. DuckDuckGo does so.
However, the freedoms to study and modify only apply to the code you
received. The one the company runs (and that you use from your Web browser)
may be different (freedom 1 guarantees this right to the company). You cannot
know therefore you cannot study the search engine you use from your Web
browser. And, of course, you cannot modify this service either since you do
not own it. As a consequence, the licenses (or absence of license!) of the
search engines in the list of Trisquel's Web browser are irrelevant.
