As far as social networks go, I prefer Facebook to Twitter because I like seeing photos from my friends' daily lives. I don't like having to exit and then return to my News Feed, though, in order to view a larger image. With Photo Zoom for Facebook, I no longer have to.
Photo Zoom for Facebook is a Chrome extension that lets you view a larger version of images just by mousing over them. Hover over a zoomable image, which includes profile pictures and photos in photo albums but not thumbnails from shared news stories, and a pop-up window appears to the left or right of your cursor with a larger version of the image.
If you come to find these pop-up images distracting, you can toggle the extension on and off using the button next to the chat bar along the bottom edge of Chrome. There is also a setting where you can have the extension turned off but zoom a photo when you hold down Shift or another key of your choosing as you mouse over it. Head to Photo Zoom for Facebook's options and click on the advanced settings tab and choose a key for the line "When off, force zoom if I'm holding down" and hit Save. There are other settings on this page, but I think that's the only one worth concerning yourself about.