I have several sites that I visit daily. All of them can be accessed by typing in the first character, or, at most, two characters - the url then appears in the

I have several sites that I visit daily. All of them can be accessed by typing in the first character, or, at most, two characters - the url then appears in the navbar, just hit <enter>. The strange thing is, every nine months or so, FF will forget one of these urls. It doesn't do it for all of them at once, just one, and it's not related to upgrades. All I have to do is enter the full url and hit enter, and things are back to normal again for that particular url for many months.