The MOBILITY support statement on the ATI website applies more to the Windows model, for which hardware vendors actually post specialized drivers for their laptops.
For Linux, the general rule should be "if it's newer than M9, then check the Release Notes. Chances are it's there". The Release Notes really do list MOBILITY FireGL ASIC support.
XFree86.0.log lists the hardware that the driver knows about. 8.12 included hardware support for quite a few MOBILITY branded ASICs as folows (you must admit it's pretty complete):
bash-2.05a$ cat /var/log/XFree86.0.log | grep -i mobility
MOBILITY FireGL 9000 (M9 4C64), MOBILITY RADEON 9000 (M9 4C66),
MOBILITY RADEON 9200 (M9+ 5C61), MOBILITY RADEON 9200 (M9+ 5C63),
MOBILITY RADEON 9600/9700 (M10/M11 4E50), RADEON 9500 (R300 4144),
MOBILITY FireGL T2/T2e (M10/M11 4E54), RADEON X300 (RV370 5B60),
MOBILITY RADEON X300 (M22 5460), MOBILITY FireGL V3100 (M22 5464),
MOBILITY RADEON X600 (M24 3150), MOBILITY RADEON X300 (M22 3152),
MOBILITY FireGL V3200 (M24 3154), RADEON X800 (R420 4A48),
FireGL X3-256 (R420 4A4D), MOBILITY RADEON 9800 (M18 4A4E),
MOBILITY RADEON X800 XT (M28 5D48), MOBILITY FireGL V5100 (M28 5D49),
MOBILITY FireGL V5000 (M26 564A), MOBILITY FireGL V5000 (M26 564B),
RADEON X700 (RV410 5E4F), MOBILITY RADEON X700 (M26 5652),
MOBILITY RADEON X700 (M26 5653), RADEON 9100 IGP (RS300 5834),
MOBILITY RADEON 9000/9100 IGP (RS300M 5835)
bash-2.05a$
/me recommends something in a MOBILITY FireGL - oh yeah
