From MozillaZine Knowledge Base
In Firefox, Find As You Type is integrated with the Find Toolbar so that when FAYT is activated, the toolbar is displayed with your typed query. The first time the Find Toolbar is opened and a match is found, the background of the toolbar's Find field is flashed to draw attention to it. This preference keeps track of whether the toolbar has “flashed” yet.
Possible values and their effects
The Find Toolbar has flashed before; don’t flash when text is found.
Flash the Find Toolbar when text is found. (Default)
Each time the Find Toolbar flashes on and off five times, the preference’s value is reduced by one. In normal operation, this means that the toolbar will only display the flashing effect once. However, you can set this preference to a negative number. That way, even though the value will be decremented, the preference will still be “true” and the flashing will occur. (Note that the flashing only occurs for the first search performed when the Find Toolbar is opened. You have to close the Find Toolbar for it to work again.) Since this is not the designed behavior, you may see unpredictable results (e.g., constant flashing, flashing when no match is found, etc.).
First checked in
Has an effect in