The Inventor of JavaScript & current CTO of Mozilla, Mr. Brendan Eich said in a blog post that the NSA is not just focused on high-tech exploits, but also specialize in inserting secret backdoor to legitimate products. Eich suggested not to blindly trust any software vendors, where the products are not Open Source. Firefox is completely open source, which means its source code is available to everyone and anybody can verify it and can detect flaws. The vendors itself are compromising their goodwill and End-to-End trust, and are becoming the part of users’ furry.
Source: https://thehackernews.com/2014/01/Firefox-open-source-browser-nsa-surveillance.html