That's becauase you have an ATI GPU, am I right?
ATI crapPU as of linux kernel 3.12 needs a proprietary firmware loaded in the
kernel for you to have native screen resolution (the same required for video
acceleration). Otherwise you will get the highest resolution supported by
your BIOS, usually 1024*768 (the same I enjoyed kicking ass on Quake 3 in
2000 x_X).
A friend in the libre community made a radeon patch in order to solve the
issue and the great jxself maintains a repo with libre 3.10 (unpatched, works
fine but support just ended, no security upgrades are planned for the
future), libre 4.1 and 4.2 (both patched. You get the native screen
resolution).
On my setup the patched libre kernel randomly and totally freezes my computer
and I need to hard reboot it. This can happen once every two days or 5 - 6
times in a day. For me, as it is, it is totally useless. Maybe you'll have
more luck.
Here the link -> https://jxself.org/linux-libre/
