A certain Stacy left her facebook open and I've got on her

It's likely that she doesn't log out very often then. Start by grabbing her session cookie (download the tamperdata addon, reload facebook with it open, scroll to the cookies section, copy everything, email it to yourself).
Once you get on your regular computer just copy the cookie you stole into the spot where yours goes and submit the request. You'll be logged in without the password.

In order to actually get said password, you should check her saved passwords on the browser. To do this you'll need her computer's password, which could be difficult to get in a short time if it's complex. If it's simple, just install some software that will be able to grab the hash that windows stores for your password and crack it by downloading password dictionaries/rainbow tables and comparing the entries there to the hash.

As an alternative, you can download a keylogger and install in on her computer. Then, set it up to send you an email containing all her keystrokes once a day or so. This in addition to the cookie will mean that you will definitely have access, as you will be logged into her session until she signs out and needs to log back in the facebook, where she will have to type in her password assuming that she didn't have it saved (which wouldn't be a problem because you've already checked browser passwords). Then you'll capture the keystrokes and have her password.

Good luck!

Open a new tab.
Go to facebook in said tab.
Go to login in screen (DONT PRESS LOGOUT)
See if password autofills out.
If it does just right click on the password field and click inspect element.
Find the parnt where it says 'Type:password' and change it to 'Type:text'.
Hit enter.
Dont refresh or exit.
Her password should now be in clear text.

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>>35341352
I am wishing this bites you in the ass in the worst way and at the worst time possible. Leave the girl alone you coward.

>>35341352
Delet sytsem tirty tew

>>35341352
Which browser? Check the settings for "saved passwords". In Firefox it'll be under Security. Chrome will have it probably under the Advanced settings.

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Change her posting style to viewed by "only me" when noone comments on her shit for months on end it will gas light her into having low self esteem