Xorg ATI video card

Hello, I am having some problems with Xorg. I thought that it was Gnome but I tried with Enlightenment and also having the same problem. The graphics are going too slow and some applications does not open like Firefox. I have an ATI Radeon 5000 video card.
That's an old page (last updated in December 2014). The page I linked to was updated last August so it should be fairly up to date.
The nvidia will work either with nvidia-driver (latest) or with nvidia-driver-340.