URL Shortener UnshortenerJS
Adds small button next to shortened URLs (t.co/bit.ly/goo.gl) on Twitter and other sites that will replace the shortened URLs with their real locations and vice-versa. Useful for when you don't want to blindly click links.
The Ultimate Popup BlockerJS
Configurable popup blocker that blocks ALL (even user-initiated) popup windows by default. But you can easily open the blocked popup or whitelist a domain, directly from the page.
FYTE /Fast YouTube Embedded/ PlayerJS
Hugely improves load speed of pages with lots of embedded Youtube videos by instantly showing clickable and immediately accessible placeholders, then the thumbnails are loaded in background. Optionally a fast simple HTML5 direct playback (720p max) can be selected if available for the video.