NoScript - https://addons.mozilla.org/en-US/firefox/addon/noscript/
This tool gives you the best available protection on the web. It allows JavaScript, Java and other executable content to run only from trusted domains of your choice, e.g. your home-banking site, guarding your "trust boundaries" against cross-site scripting attacks (XSS), cross-zone DNS rebinding / CSRF attacks (router hacking), and Clickjacking attempts, thanks to its unique ClearClick technology. It also implements the DoNotTrack tracking opt-out proposal by default.
uBlock Origin
https://addons.mozilla.org/en-US/firefox/addon/ublock-origin/
https://github.com/gorhill/uBlock#ublock-origin
An efficient blocker add-on for various browsers. Fast, potent, and lean. uBlock Origin is NOT an "ad blocker": it is a wide-spectrum blocker -- which happens to be able to function as a mere "ad blocker". The default behavior of uBlock Origin when newly installed is to block ads, trackers and malware sites -- through EasyList, EasyPrivacy, Peter Lowe’s ad/tracking/malware servers, various lists of malware sites, and uBlock Origin's own filter lists.
Self-Destructing Cookies
https://addons.mozilla.org/en-US/firefox/addon/self-destructing-cookies/
Fix the web. Gets rid of a site's cookies and LocalStorage as soon as you close its tabs. Protects against trackers and zombie-cookies. Trustworthy services can be whitelisted. Self-Destructing Cookies automatically removes cookies when they are no longer used by open browser tabs. With the cookies, lingering sessions, as well as information used to spy on you, will be expunged. Websites will only be permitted to identify you while you actually use them and can not stalk you across the entire web. This is the closest you will get to cookieless browsing without breaking every second site or tedious micromanaging.