The Tor Browser has many customizations and security features, but Tor itself is baked right in. The Mullvad Browser, made by the eponymous VPN company and the Tor Project, makes the app available without the network.
Our goal was to give users the privacy protections of Tor Browser without Tor. For instance, the Mullvad Browser applies a "hide-in-the-crowd" approach to online privacy by creating a similar fingerprint for all of its users. The browser's 'out-of-the-box' configurations and settings will mask many parameters and features commonly used to extract information from a person's device that can make them identifiable, including fonts, rendered content, and several hardware APIs. By default, Mullvad Browser has private mode enabled, blocks third-party trackers and cookies, and makes it easy to delete cookies between visiting pages during the same session.
The Mullvad Browser is another option for internet users who are looking for a privacy browser that doesn't need a bunch of extensions and plugins to enhance their privacy and reduce the factors that can accidentally de-anonymize themselves. And unlike other browsers on the market, Mullvad Browser's business model does not rely on capitalizing on users' behavioral data.
The tl;dr: it does the privacy-protecting things Firefox can't because if Firefox did them everyone would complain about having to log into their Evil Corp account every time they go back to its website or whatever.