The new Firefox 58 is the first update to Firefox Quantum, as the company calls its largely revamped browser. It brings along many under-the-hood upgrades that speed up many facets of browser, including a JavaScript performance boost of up to a third.
More technically Mozilla has added support for Windows' Off-Main-Thread Painting which allows rendering to be done on a separate thread. Along with better multithread support Firefox 58 includes the previously used Tracking Protection tech that speeds up loading of pages potentially even more.
The updates also added support for Progressive Web Apps (PWA) on Android.
If you want to give the new version a try, download Firefox 58 for Windows here.