Web Browsers

Settings

browser.sessionstore.interval

See: https://www.servethehome.com/firefox-is-eating-your-ssd-here-is-how-to-fix-it/
Set to 150000 to store the session every 150000ms (150 seconds) to avoid writing to disk too often.

Privacy

• Adblock Plus
  Block advertisements
• BugMeNot
  Login using shared accounts
• ublock origin
  Block unwanted third-party scripts and cookies
• privacy badger
  Protects your privacy
• Ghostery
  Anti-tracking
• ShareMeNot
  Removes social sharing buttons and prevents their cookies
• HTTPS Everywhere
  Enables HTTPS encryption automatically on sites that are known to support it, even when you type URLs or follow links that omit the https: prefix.

Security

• LastPass Password Manager
  Password Manager

Usability

• Tree Style Tab
  Tabs on the left
• fox input
  Ctrl + i cycles focus through the page's text input boxes.
• Classic Compact
  Allows compact UI with advanced settings.
• Classic Theme Restorer
  Squared tabs, appmenu, add-on bar, small button view and many more 'old' features for Firefox 29+ (Windows / MacOSX / Linux).
• FLST
  Switch between current and last selected tab with click or Ctrl + .
• SmoothWheel
  Scroll smoothly
• Show Profile
  Displays the name of the Firefox profile on window title or customized locations. Only useful if you have multiple Firefox profiles (I have many. See why here.).
• ProCon Latte Content Filter
  Simple whitelist / blacklist site filter. Not really secure, but can help prevent you from browsing sites you don't want to browse within a specific browser profile.
• Stylish
  Lets you easily install themes / CSS modifications for sites.
• Restartless Restart
  Adds a quick method (File->Restart) to restart the browser.
• Nuke Anything Enhanced
  Allows you to hide almost anything via context menu 'Remove Object'. Great when you just want to print a portion of the page.
• BarTab Lite
  Keeps tabs from loading until you activate them.

Development

• TotalValidator
• Firebug

Other

• DownloadHelper
• FlashBlock
• GreaseMonkey
• RES
• Restartless Restart
• UAControl (requirement of pipelight)