By default, when you scroll the mouse wheel, the web page is scrolled the same number of lines no matter how many times you have already scrolled it. But, if you have scrolled the page a certain number of times in a short period, probably you are looking for something far below or above, and accelerating may be helpful.
Scroll acceleration was implemented by Mozilla intern Margaret Leibovic, very early in Firefox 3.6 development, but finally turned off because it could conflict with mouse driver based acceleration, detecting it was out of scope. So it was postponed for next versions.
But the feature is there, and I have found it very useful, and have become used to it. To enable it, go to about:config to access the advanced preferences. Then look for mousewheel.acceleration.start, and set it to the number of successive mouse scrolls that will trigger acceleration. I found 3 to be a good number for me. Then, set mousewheel.acceleration.factor to how many times faster you want to scroll. I tried and liked 5.
With Firefox’s default setting it took me 14 mouse scrolls to scroll Margaret’s post (with 30+ comments), versus 6 with acceleration.
If you try this setting, please share the values you found to work best for you.