Yeah! for Twitter v1.1.3
Extension that adds a "Yeah!" button to Twitter. Essentially, it's a public Like button. It doesn't send spammy images into replies, instead it saves your Yeahs into a shared database. Everyone can see who Yeahed a tweet, and what tweets person Yeahed.
This extension supports both new Twitter and OldTwitter!
This extension is open source: https://github.com/dimdenGD/YeahTwitter/