UPDATE:

1. Type about:config in Firefox’s address bar
2. Type: mousewheel.default.delta_multiplier_y in the filter box
3. Change mousewheel.default.delta_multiplier_y’s value to 200 if you want to double it. I use 400.

1. Type about:config in firefox address bar 2. Optional Type: mousewheel.withnokey in the filter box 3. Set mousewheel.withnokey.sysnumlines to false This makes Firefox use its own setting instead of the system-wide setting.

4. Change mousewheel.withnokey.numlines to how many lines you want to scroll at a time. I use 8

Source: http://episteme.arstechnica.com/groupee/forums/a/tpc/f/99609816/m/480004345731