Short version: Radeon GPUs are all terrible with free/libre software. You'll
have to either get a somewhat old Nvidia card to replace it, or just deal
with not having hardware acceleration; and remember, next time, to get
something with Intel integrated graphics, which is the best choice.
Long version:
All AMD/ATI (Radeon) GPUs work only in 2-D, and at least some of them don't
even support 2-D hardware acceleration, without proprietary firmware blobs.
Because they're proprietary, they are of course not included in Trisquel. You
would have the same problem with your GPU in Debian if you didn't install
this blob or the proprietary driver from the non-free repository.
To solve the lack of hardware acceleration your current laptop, you would
need to replace the Radeon GPU with an Nvidia card that is supported
sufficiently by Nouveau and will fit in your laptop. There is no other
solution, I'm afraid. You could start with Think Penguin;[1] they sell one
Nvidia card that works well with Nouveau. If that's no good for your laptop,
you'll have to do some research to make sure you're getting something that
has good enough Nouveau support. There's a table of what features are
supported for what cards on the Nouveau project website.[2]
Regarding the heating issue: if your laptop's fan is having a hard time
keeping up with the CPU's heating, maybe you should invest in a laptop
cooler. I once got one for a laptop that had an almost useless fan (mostly
because of dust that had accumulated), and it made a world of difference.
Alternatively, since it's only overheating because the CPU's doing so much
work, you might try underclocking, though I don't know anything about how to
do that.
[1] http://libre.thinkpenguin.com
[2] http://nouveau.freedesktop.org/wiki/FeatureMatrix/
