From MozillaZine Knowledge Base
Normally, scrolling with the mousewheel will scroll the entire page. If the mouse cursor is over a scrollable element on the page, that element will scroll instead, until it can scroll no more, and then the entire page will continue scrolling. However, this can be disruptive if a user is scrolling a page and happens to mouseover another scrollable element (e.g., a form select dropdown or multi-line text field). Conversely, if a user is scrolling through a dropdown or text field and hits the top or bottom, having the entire page start moving again can be annoying.
To address these common cases, every use of the mousewheel is considered a “transaction.” Within a transaction, only one element is scrolled, whether it be the entire page or a dropdown menu. This preference controls how long to wait after the user stops scrolling before the transaction is considered complete; if the user starts scrolling again within this time period without moving the mouse, the same element will be scrolled.
Possible values and their effects
An integer determining the number of milliseconds to wait until ending the current mousewheel transaction. Default value is 1500 (1.5 seconds).
First checked in
Has an effect in