This has been eloquently addressed by Tor veteran Mike Perry:[1] Concerns about Javascript are rooted in two avenues: 1. Fingerprinting concerns. 2. Zero-day

This has been eloquently addressed by Tor veteran Mike Perry:[1] Concerns about Javascript are rooted in two avenues: 1. Fingerprinting concerns. 2. Zero-day exploits against Firefox. The reason we feel that leaving Javascript enabled trumps these concerns is: 1. We want enough people to actually use Tor Browser such that it becomes less interesting that you're a Tor user. We have plenty of academic research and mathematical proofs that tell us quite clearly that the more people use Tor, the better the privacy, anonymity, and traffic analysis resistance properties will become. In fact, my personal goal is to grab the entire "Do Not Track" userbase from Mozilla. That userbase is probably well in excess of 12.5 million people: http://www.techworld.com.au/article/400248/ http://www.techworld.com.au/article/400248/ I do not believe we can capture that userbase if we ship a JS-disabled-by-default browser. 2. Exploitable vulnerabilities can be anywhere in the browser, not just in the JS interpreter. We disable and/or click-to-play the known major vectors, but the best solutions here are providing bug bounties (Mozilla does this; we should too, if we had any money) and sandboxing systems (Seatbelt, AppArmor, SELinux). [1] : https://lists.torproject.org/pipermail/tor-talk/2012-May/024227.html https://lists.torproject.org/pipermail/tor-talk/2012-May/024...