Todayapp, bringing Chat Heads to the platform, although it's in a limited way. The new feature will only work while you're actively using the Facebook app.
Chat Heads will slowly roll out over the coming weeks to iOS users, but if you're the impatient kind who isn't afraid to edit some files on your device, you're going to want to head on over to this post on iMore.
The post will walk you through the process of saving, viewing, and editing a PLIST file from the Facebook app; you then add or change a single value in the file, load it back onto your device, then close out the Facebook app and relaunch it. You'll then be able to take advantage of Chat Heads on iOS right now. Of course you'll need to be running version 6.0 of the Facebook app on your iOS device in order for this to work.
The guide also includes a workaround to unlock the new Stickers feature. The solution to unlock Stickers requires a proxy, which isn't something everyone is going to want to set up and use.
I enabled Chat Heads on my iPhone 5 by using iExplorer to grab the PLIST file and Xcode to edit it. The entire process took less time than it takes to brew a cup of coffee at a fancy coffee shop. Not being a big fan of Stickers, I opted to stop with the Chat Heads trick and simply wait for Facebook to enable Stickers on my account.