From MozillaZine Knowledge Base
Firefox 3 introduced a number of improvements to the Location Bar. Among them were changes to how sites are ordered in the dropdown menu. Firefox takes into account how frequently and how recently sites in the browser history were visited, combining them into a statistic called “frecency.” The frecency of sites is calculated when the browser is idle. The way frecency is computed can be tweaked by a number of preferences.
This preference determines how long the browser must be idle before starting frecency calculations in the background.
Possible values and their effects
The number of milliseconds of idle time to pass before starting frecency calculations. Default value is 60000 (1 minute).
First checked in
Has an effect in