People will fall for anything. There is a scam going around twitter and other social networking sites telling users that if they follow a certain shortened URL (see here for more on the dangers of shrotened URLS), they can then download a cracked version of Firefox 4.0 or a key generator for Mozilla Firefox 4.0.
This of course only leads you to a place to download all kinds of malware onto your computer.
This is ridiculous, as Mozilla Firefox is Open Source (as in free, always!)
You can download the REAL Firefox 4.0 beta from the Firefox site FREE! Keep in mind it IS a beta, there WILL be bugs.