Its concept is like FlashGet (or similar download managers),
though does not work as well.
Firefox is not used for being fast. It is not faster than IE.
However, due to environmental (of networks) issues. Its hard to
tell the exact abilities of browsers.
Apple recently released Safari 3 for Windows XP and Vista in beta
versions.
Its webpage has some graphs comparing Firefox2, IE7, Safari3, and
Opera in terms of HTML, Java and some others.
I personally don't like safari, and am sticking with FF. If you are
interested, check the statics out and see if it applies to
you.
http://www.apple.com/safari/