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/).
<p>To prevent Tails from running out of memory and crashing, download very big files to the <em>Persistent/Tor Browser</em> folder. All the files that you download outside of the Persistent Storage are stored in memory (RAM), which is more limited.</p>
It is impossible to hide to the websites that you visit that you are using Tor, because the [list of exit nodes of the Tor network is public](https://metrics.torproject.org/exonerator.html).
The anonymity provided by *Tor Browser* works by making all users look the same to make it impossible to know who is who among the millions of users of *Tor Browser*.
Tails tries to make it as difficult as possible for websites to distinguish Tails users from other users of *Tor Browser*. If it was possible for a website to determine whether you are a user of *Tor Browser* inside or outside of Tails, this would provide a little bit more information about you and reduce your anonymity.
The websites that you visit can retrieve a lot of information about your browser, whether it's *Tor Browser* or a regular browser. This information is called the *fingerprint* of the browser and includes the name and version of the browser, the size of the window, the time zone, the available fonts, etc.
To make it difficult to distinguish Tails users from other users of *Tor Browser*, *Tor Browser* in Tails tries to provide the same information as *Tor Browser* on other operating systems.
