Noscript

Noscript: the best security you can have in your browser! Only allow active content on website you trust and protect yourself against XSS and Clickjacking attacks, Spectre, Meltdown and other JavaScript exploits.
FAQ: https://noscript.net/faq
Forum: https://noscript.net/forum
“Giorgio Maone’s NoScript script-blocking plug-in is the one-and-only Firefox add-on I consider mandatory.” – CNET News
More information on https://en.wikipedia.org/wiki/NoScript