Firefox add-ons

Blocking

 * 1) Block sites by regex
 * 2) uBlock. Blocks more than just ads.
 * 3) uBlock Origin. Blocks more than just ads. Supports many third party lists, and you can make your own, block a page element, and more. Smaller and more efficient than other blockers.
 * 4) Blocksi blocks websites

Privacy

 * 1) Ghostery. Tells you how many third-parties are tracking you.

Screen capture

 * 1) Awesome screen shot. Lets you do basic edits on a screen before copying to clipboard, or saving to a file. Edits: Boxes, circles, lines, text, in different colors.