This post is mostly for my reference, but hopefully it is useful to others as well. :)

Extensions:

Extension Name	Description	License	Development	Restart Required
BetterPrivacy	Removes Flash "Super-Cookies" / LSOs (Local Shared Objects)	Freeware	Inactive	Yes
cliget	Download protected files using curl, wget, or aria2.	MPL 1.1	Active	No
Cookie Controller	Buttons for managing cookies, cookie permissions, and site cookie exceptions.	MPL 2.0	Active	Yes
DuckDuckGo Plus	Adds DuckDuckGo as the default address bar, search bar and right-click search engine.	Apache 2.0	Active	No
Greasemonkey	A userscript manager.	MIT/X11	Active	Yes
HTTPS-Everywhere	Encrypt the Web! Automatically use HTTPS security on many sites.	GPLv3	Active	Yes
Policeman	Can be used as a replacement for RequestPolicy and NoScript. Policeman gives you precise control over what web requests are allowed.	GPLv3	Active	No
Privacy Badger	Protects privacy by evaluating third-party sites and blocking those that appear to be tracking you.	GPLv3	Active	No
Random Agent Spoofer	Rotates complete browser profiles ( from real browsers / devices ) at a user defined time interval. It includes many extra privacy enhancing options. Note: The Github version has more features which AMO won't allow.	GPLv3	Active	No
Reddit Enhancement Suite	A suite of tools to enhance Reddit.	GPLv3	Active	No
Self-Destructing Cookies	Protects against trackers and zombie-cookies. Gets rid of a site's cookies and LocalStorage as soon as you close its tabs.	GPLv2	Active	No
Smart Referer	Send referers only when staying on the same domain.	WTFPL	Active	No
SSleuth	SSleuth ranks an established SSL/TLS connection and gives a brief summary of the cipher suite, certificate and other SSL/TLS parameters.	GPLv3	Active	No
The Addon Bar (restored)	Restores the Addon bar.	MIT/X11	Active	No
uBlock	A excellent light-weight blocker that was recently ported to Firefox.	GPLv3	Active	No

Userscripts:

Name	Description	License	Development
AdsBypasser	Skips count-downs/continue pages and more.	BSD	Active
Bigger Twitch	Stretches the twitch player so it uses as much space as possible.	MIT/X11	Active
Bypass YouTube age verification Improved	Bypasses YouTube age verification without logging in.	GPLv3	Active
DuckDuckGo Extended	Adds a customizable list of quick links to other search engines.	MIT/X11	Active
Google Hit Hider by Domain (Search Filter / Block Sites)	Block unwanted sites from showing up on search results at Google, DuckDuckGo, & Startpage.	BSD	Active
Hide unwanted streams on Twitch	Blocks channels, games, etc that you are not interested in.	MIT/X11	Active
ViewTube	Watch videos on various sites without needing Flash.	GPLv3	Active
Youtube Video Ratings Bar with Power Meter	Places a ratings bar beneath video thumbnails and indicates viewer 'enthusiasm' alongside likes and dislikes.	CC BY-NC-SA 3.0	Active

If you have interesting Firefox extensions or Userscripts (preferably open source), please feel free to post them in the comments section below.