mb850063@... wrote:

> I installed the amd firmware.
> 
> Then, as root, the desktop worked with no slowlyness problem, videos
> worked normally and synchronized with the sound (yet before, they worked
> better than as user).

Can you check the prmissions and if the user is in the video group?

$ ls -al /dev/dri/
total 0
drwxr-xr-x   3 root root        100 Jan 16 21:20 .
drwxr-xr-x  20 root root      14420 Jan 24 20:30 ..
drwxr-xr-x   2 root root         80 Jan 16 21:20 by-path
crw-rw----+  1 root video  226,   0 Jan 25 13:50 card0
crw-rw----+  1 root render 226, 128 Jan 16 21:20 renderD128