Apart from retaining XUL support, it also:
* Disabled Encrypted Media Extensions (EME)
* Disabled Web Runtime (deprecated as of 2015)
* Removed Pocket
* Removed Telemetry
* Removed data collection
* Removed startup profiling
* Allow running of all 64-Bit NPAPI plugins
* Allow running of unsigned extensions
* Removal of Sponsored Tiles on New Tab Page
* Addition of Duplicate Tab option
* Locale selector in about:preferences > General
Judging by that feature list alone, this seems like a browser that respects user privacy, is against DRM and advertising to its users, and gives the user the power to run any extension they want instead of limiting them to running only signed extensions.