Today I browsed the addons repo and found some interesting ones I didn't know about.
* Hello/WebRTC is amazing but as it enables direct IP connections, it may carry a privacy issue.Disable WebRTChttps://addons.mozilla.org/en-US/firefo ... dl-hotness
Source code is available here: https://github.com/ChrisAntaki/disable-webrtc-firefox
If there's an issue with the plugin, please let me know: https://github.com/ChrisAntaki/disable- ... fox/issues
Edit: There's a pref suggested in the addon comments...
In about:config, you can set media.peerconnection.ice.default_address_only=true. No need to completely disable WebRTC.
"Disable Visited Linkshttps://addons.mozilla.org/en-us/firefo ... l-othersby
SoundCloud Downloader - SoundGrabhttps://addons.mozilla.org/en-US/firefo ... b-dl-users
Did you know that visited link styles allow websites to elicit web history? 
This plugin cleanly disables visited link styles.
Source code is available here: https://github.com/ChrisAntaki/visited-links-firefox
Adds download link/button to all SoundCloud tracks and sets.EPUBReaderhttps://addons.mozilla.org/en-US/firefo ... b-dl-users
With EPUBReader you can read ePub files just in Firefox. No additional software needed!
And two addons more I don't know really how to tell if they are of trust...ZenMate Security & Privacy VPNhttps://addons.mozilla.org/en-US/firefo ... b-dl-users
Unblock the web and change your IP with 4 locations across the globe. ZenMate secures your browsing with encryption - protecting you from hackers, snoopers and data thieves who prey on unsecure connections.anonymoXhttps://addons.mozilla.org/en-US/firefo ... 91efa10e2c
Easy anonymous web browsing.
– Change your IP-Address and country
– Visit blocked or censored websites.
– Delete cookies, show your public ip, and more
We provide the proxy servers, no external proxies or other programs required