[Tor Browser 10.0.4](https://blog.torproject.org/new-release-tor-browser-1004) upgrades to [Firefox ESR 78.4.1](https://www.mozilla.org/firefox/78.4.1/releasenotes/), which fixes https://www.mozilla.org/en-US/security/advisories/mfsa2020-49/. People using the Safer or Safest security level of Tor Browser are not affected because the feature of JavaScript that is affected (the just-in-time compilation) is disabled in these security levels.