Firefox: If you regularly mistype your password because you're in a rush, Visual Hashing will turn your password into a coloured hash to you can immediately see whether you've typed it correctly or not.
As you type your password, Visual Hashing displays four coloured boxes in the password field. As you type, the colours change, and your password will have a specific colour combination. That way, if you mistype it, you'll know right away, because the colours will be all off.
See the above image, for example -- that's the hash for
123456789 (no, that's not my real password -- geez!). Were I to add a
0 to the end, it would be four different shades of green instead.
Obviously, you wouldn't want to use this extension if someone were looking over your shoulder, in case they download the extension themselves and learn all your passwords by the colours they saw, but it can be handy for your home desktop, if you're the type to bang out your passwords a little too quickly.
Visual Hashing is a free extension, works wherever Firefox does.
Visual Hashing [Mozilla Add-Ons]