A friend set me a link on my facebook as a joke, but I never found it funny. I logs you out of many websites if of course you are logged into them, I think it's very scary that just navigating to a website can do that.

I guess I'd like to know how this can occur and how to block this kind of thing from happening elsewhere.

the websites it logs you out of are...

AOL
Amazon
Blogger
Delicious
DeviantART
DreamHost
Dropbox
eBay
Gandi
GitHub
GMail
Google
Hulu
Instapaper
Linode
LiveJournal
MySpace
NetFlix
New York Times
Newegg
Photobucket
Skype
Slashdot
SoundCloud
Steam Community
Steam Store
ThinkGeek
Threadless
Tumblr
Vimeo
Wikipedia
Windows Live
Woot
Wordpress
Yahoo!
YouTube

And this is the link, but like I said,

don't go there unless you don't care about getting logged out of websites

.

http://superlogout.com/

why scary?
Any logout from any website is just a link you click. Which submits a request to a webserver somewhere.
Javascript can submit requests to webservers, so can a lot of other things.

Of course it's possible to write a logout system that requires active cooperation from the user, but that'd just piss off those users.
It'd come down to having to enter your password to log off, rather pointless is it?

I think navigating to a site and unwittingly being logged out of several others without verification could be quite a pain in the butt.

I imagine that that is the entire point of the site, to be one giant PIA.

hxxps://www.daniweb.com/members/logout