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 controls how often the tab strip scrolls (by a defined amount) when its arrow buttons are clicked and held, or when a dragged tab is held over the buttons.
Possible values and their effects
A positive integer that determines how many milliseconds to wait before scrolling the tab strip by another increment. (Default: 150)
First checked in
Has an effect in