From MozillaZine Knowledge Base
Firefox 2.0 introduced a number of refinements to its tabbed browsing UI. One area addressed is that of “tab overflow,” or how a large number of tabs is handled: the user can now scroll the tab strip horizontally to see all available tabs. This preference specifies how quickly the strip scrolls when the arrow buttons are pressed or when a tab is dragged over the arrows.
Possible values and their effects
A positive integer that determines how many pixels to scroll at a time when scrolling the tab strip’s scrollbox. (Default: 20)
First checked in
Has an effect in