Thanks to Denis 'GNUtoo' Carikli for his patch [0] to make the radeon kernel
module work again in free distros and not just fall over and die when the
proprietary firmware isn't there. I've made these changes to Linux-libre
version 4.1.4 in my APT repository. If you have such a card you may want to
look into this in order to have proper screen resolution, etc. I've talked to
quidam about getting it into the Trisquel kernel. Hopefully that will be part
of Trisquel 7.1.
In the meantime, information about using the repository can be found at
https://jxself.org/linux-libre/
[0] http://www.fsfla.org/pipermail/linux-libre/2015-July/003080.html