Try to visit by typing only one letter in the address bar of Firefox and then press Enter key, so the Firefox try to search the most fitted URL for the word (One charactor), usually Firefox query Google to do the job, and here is the result of mine:

z: http://z/ an auto web site
y: http://messenger.yahoo.com/
x: http://www.paypal.com/cgi-bin/webscr I could see it redirecting from http://x/
w: http://www.starwoodhotels.com/whotels/index.html
v: http://vforvendetta.warnerbros.com/
u: http://www.arizona.edu/
t: http://att.sbc.com/gen/landing-pages?pid=3308 AT&T
s: http://www.mcdonalds.com/
r: http://www.r-project.org/
q: http://q/
p: http://www.sloan.org/main.shtml
o: http://www.oreilly.com/
n: http://www.kn.pacbell.com/wired/bluewebn/ AT&T
m: http://www.tamu.edu/
l: http://www.coe.int/
k: http://www.kmart.com/home.jsp
j: http://www.jenniferlopez.com/
i: http://www.apple.com/itunes/
h: http://www.h-net.org/
g: http://mail.google.com/mail/
f: http://www.fuckedcompany.com/
e: http://www.eonline.com/
d: http://www.dlink.com/
c: http://www.c-span.org/
b: http://www.btselem.org/index.asp
a: http://www.apple.com/

Tricks for quick browsing:
g, and then will go for your gmail
a, for apple and i for itune
o, for oreilly books
y, for yahoo messenger
x, for money paypal

Environment: Firefox 1.5.0_3, From China Shanghai, May 18, 2006