*[Tor Browser](https://www.torproject.org)* is a web browser based on [Mozilla Firefox](https://www.firefox.com/) but configured to protect your privacy.
Security vulnerabilities in JavaScript have been used to [deanonymize Tor Browser in the past](https://arstechnica.com/information-technology/2013/08/attackers-wield-firefox-exploit-to-uncloak-anonymous-tor-users/).
Refer to the [[fingerprint section of our list of known issues |support/known_issues#fingerprint]] to know if there are differences between the fingerprints of *Tor Browser* inside and outside of Tails.
That is why JavaScript is enabled by default but *Tor Browser* disables all potentially dangerous JavaScript. We consider this as a necessary compromise between security and usability.
<p>To understand better the behavior of <i>Tor Browser</i>, for example, regarding JavaScript and cookies, you can refer to the <a href="https://2019.www.torproject.org/projects/torbrowser/design/"> <i>Tor Browser</i> design document</a>.</p>
You can change the security level of *Tor Browser* to disable browser features as a trade-off between security and usability.For example, you can set the security level to *Safest* to disable JavaScript completely.
<p>You can safely disregard the message, "Your browser is being managed by your organization," which appears in the <i>Tor Browser</i> preferences.</p>
<p>All this message means is that the automatic updates feature of <i>Tor Browser</i> has been disabled. This is done intentionally in Tails to make sure that no security feature or configuration gets broken by automatic updates of <i>Tor Browser</i>.</p>
The letterboxing feature of *Tor Browser* helps to prevent websites from identifying your browser based on the size of its window.Without letterboxing, websites could use the size of the browser window to track visitors or weaken your anonymity.
The letterboxing feature of *Tor Browser* works by adding gray margins to the browser window when the window is resized. The webpage remains as close as possible to the desired size without revealing the actual size of the window.