In file: ~/.config/xfce4/mcs_settings/mouse.xml; the data type for
"Mouse/Acceleration" and "Mouse/Threshold" are set ton 'int'. The GUI tool thus
only allow integer values, which with some hardware is not precise enough. 

xset says:
    To set mouse acceleration and threshold:
         m [acc_mult[/acc_div] [thr]]    m default

I could set correctly my new mouse using an xset wrapper in ~/Desktop/Autostart
but it would be fine that mouse config tool would allow either:

- to enter a value manually, possibly decimal or fraction
- to show current value, not just a position on a ruler without graduation
- an hybrid ruler + numerical inc:dec arrows (seems the best choice imho)

my former mouse was ok with "integer" values, I guess the importance of
precision is higly dependent of the hardware, the model etc.

Reproducible: Always
Steps to Reproduce:
1. run xfce4-setting-show
2. go in mouse settings

Actual Results:  
no way to have the mouse acceleration set with enough precision

Expected Results:  
being able to set decimal values for acceleration, and possibly treshold values.