Alphabetical order, Chrome browser (I actually use more, but thise are the essentials): AdBlock, Better Popup Blocker, Chime, Disconnect, Extensions Manager (because the default sucks), FlashBlock, HTTPS Everywhere, Kill Evil, LastPass, Markdown Preview (.md viewer), OneTab, Personal Blocklist, RSS Live Links (I like my RSS on my own computer), Stoppity Poppity, Stylebot, Stylish, Terms of Service; Didn't Read (ToS;DR), Turn Off The Lights, Unsocialize, WOT (Web Of Trust)

NoScript, AdBlock Plus, Webdeveloper Toolbar, Screengrab, Color Picker, YSlow, Firebug

Stayfocused is my prime choice. Lastpass and Adblock also deserve mention of course.

Essential: RequestPolicy, NoScript, DownThemAll, HTTPS-Everywhere, Status-4-Evar, Switch to Tab no more

Useful on occasion: Firebug, ReloadEvery, Resurrect Pages, User Agent Switcher, View Dependencies

Edit This Cookie, Session Buddy, Proxy Switchy, Reload Extensions, Personal Blocklist, Page Monitor, Adblock Plus, OnePassword. These are must have for me.

Adblock Plus, Ghostery, Disconnect, Pocket, Google Cast, HN Special, new metro tab

Adblock Plus, Delicious Bookmarks, Flashblock, HN Utility Suite, X-notifier

Keepass, Ghostery, DownThemAll, Adblock Plus, NoScript and Greasemonkey.

Firefox here. Livereload, Pushbullet, Adblock, HTTPS Everywhere

Vimium

Firebug, NoScript