Thumbnail Rating Bar for YouTube™ - Displays a rating bar (likes/dislikes) on the bottom of every YouTube™ video thumbnail.
HTTrack - HTTrack is a free (GPL, libre/free software) and easy-to-use offline browser utility.
Greasy Fork - A site for user scripts.
SingleFile - Save a complete page into a single HTML file
OpenUserJS - Download userscripts to enhance your browser.
Web ScrapBook - A browser extension that captures the web page faithfully with highly customizable configurations.