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.
When highlighting matched text, only the first portion of the text is checked. This preference determines how many characters into the text will be searched for matches.
Possible values and their effects
A non-negative integer determining how much of the text to search for matched text, specified as the number of characters from the beginning. Default is 200.
First checked in
Has an effect in