"What would you say is the most well kept Firefox secret? Or,
put another way, what's the most useful aspect of Firefox that most
users don't know about?
"Kevin Yank: The one feature I show people over
and over is the find-as-you-type search. While viewing any Web
page, hit the slash (/) key (or Ctrl-F if you need something easier
to remember), then start typing the text you'd like to find. As you
type, Firefox will instantly scroll to and highlight the first
match in the page. If you type something that can't be found in the
page, the box you're typing in will turn red. Once you've found the
text you want, you can hit F3 repeatedly to jump through all the
matches in the page..."