This is currently where Mozilla Firefox is going, and they've released a public preview of where they believe the web will be when they release it. The main drawbacks of installing this are definitely the lack of plugin/extension support and coming across possible bugs.
You can install this version in parallel to other versions of Firefox (I'm running 4.x). But to be honest, I hardly see any real new features in this release of Firefox.
The current release plan for Firefox versions is Aurora, then Beta and Final.
Mozilla promises to improve on performance with future Firefox versions and this is the starting point.
Firefox Aurora Beta is licensed as Freeware for Windows (32-bit and 64-bit) operating system / platform from internet browsers without restrictions. Firefox Aurora Beta 51.0 is available to all software users as a free download (Freeware).
Compatibility with this software may vary, but will generally run fine under Microsoft Windows 10, 8, 8.1, 7, Vista and XP on either a 32-bit or 64-bit setup. A separate x64 version may be available from Mozilla.
We have tested Firefox Aurora Beta 51.0 against malware with several different programs. We certify that this program is clean of viruses, malware and trojans. [Read more]