Here is a compiled list of the most useful extensions/applications available on the web.
Ad Block : Blocks ads all over the web.
Auto Patch Work : Automatically loads the next page and inserts into current page when you reach the end of the page. like AutoPagerize.
Facebook Disconnect : Stop Facebook from tracking the webpages you go to.
Google Dictionary : You double click a word, it defines it.
Invisible Hand : Automatically get the lowest price on whatever you’re buying.
CouponFollow : Find every coupon code for you… automatically !
Privacy Fix : Manages all of your privacy settings in one place.
Proxtube : Helps you to unblock region locked videos on YouTube.
Social Fixer : Social Fixer for Facebook fixes annoyances, adds features, and enhances existing functionality to make FB more fun and efficient
Honey : Automatically find and try coupon codes with 1-click. Works at over 100 top stores in the US, Canada and UK.
Reddit Enhancement Suite : A group of enhancements for browsing Reddit
Hover Zoom : Move your mouse cursor over thumbnails to view images in their full size without loading a new page.
Youtube Ratings Preview : This modifies YouTube to allow you to see the rating of related videos before you click on them.
Amazon Wish List Button : Add products from any website to your Amazon Wish List.
Turn off the lights: The entire page will be fading to dark, so you can watch the video as if you were in the cinema.
Stayfocusd : Increases your productivity by limiting the amount of time that you can spend on time-wasting websites.
Ghostery : Protect your privacy. See who’s tracking your web browsing
Imgur The World : Easy way to put online images on imgur. Right click an image or click adress icon and get the imgur link directly in clipboard.
Stop Autoplay for YouTube : Stops YouTube autoplay but allows pre-buffering.
Speed Dial : Replace Chrome new tab with your predefined visual bookmarks.
LastPass : A free password manager and form filler.
SmoothScroll : Scrolls the websites smoothly when scrolling with the mouse wheel or the keyboard
Smooth Gestures : Allows you to move the mouse while holding the right mouse button to trigger actions, such as page navigation or tab management.