micrOdOts.org / ramblings [of the ABsurd]

Go to about:config
Change mousewheel.withnokey.sysnumlines to false by doubleclicking.
This value sets whether the wheel's speed will be as in the system settings.

Change mousewheel.withnokey.numlines to a number as to how fast you like; I use 6.

Very useful in linux, since Firefox is a Gnome application
and Gnome does not have a mouse wheel adjustment;
it is hardcoded(!)