Trisquel is actually downstream of a project that includes non-free software.
Ultimately helping fix distributions which include non-free software helps
just as much if not more than helping just Trisquel. You can't really fix
non-free bug because a non-free program is non-free.
But if you back up many bugs are actually upstream of Ubuntu and similar
distributions. These distributions get the code from elsewhere and its there
that many of these bugs are actually getting fixed.
If you submit a bug fix for Trisquel chances are it'll end up going to Ubuntu
and then upstream to the component in which needs to be fixed. IE the
mainline kernel project for instance.
It makes the most sense to test as far upstream as possible and submit bugs
there rather than here.
