Which browser is a modified Mozilla Firefox ESR bundled with Tor software?

The Tor Browser is a modified Mozilla Firefox ESR browser bundled with Tor software.

Tor Browser combines a customized Firefox Extended Support Release with components such as the Tor proxy, Tor Launcher, TorButton, and NoScript. Together, these tools route browsing through the Tor network and apply privacy and security settings designed to reduce tracking, surveillance, and browser fingerprinting.

The project began as the Tor Browser Bundle and was announced in January 2008. Its Firefox foundation is not accidental: Firefox’s open-source code provides a mature browser platform, while the Tor Project adds patches and configuration changes intended to make users look more alike and limit information that websites can collect.

Tor Browser is not simply Firefox with a proxy switch enabled. Using an ordinary browser through Tor can expose identifying details through scripts, plugins, fonts, or browser characteristics. That is why the Tor Project recommends its specially configured browser. It is available for major desktop platforms and Android, although releases may use different Firefox ESR foundations over time.