From MozillaZine Knowledge Base
In Firefox 3, the Location Bar received a number of improvements. Among those improvements was the move to a XUL richlistbox widget for the auto-complete dropdown. This allowed styled URL/title information, favicons, and highlighted match information. This preference determines how many entries should appear (at most) in the dropdown.
Possible values and their effects
A non-negative integer corresponding to the maximum number of entries that can appear in the Location Bar auto-complete dropdown. Default is 12.
First checked in
Has an effect in