Hi netravelr,
never had this isssue. The mouse speed in the menu is the same as in your OS.
The ingame mouse speed may by using raw mouse data, because of the mouse capturing.
A fast workaround may be to set your dpi or mouse speed higher in your OS.
Do you use a special kind of mouse?
What OS, browser are you using?
What mouse are you using and what settings?
Will add a mouse speed option today.