Marcin Juszkiewicz, a prolific ARM Linux developer, received an APM Mustang board from AppliedMicro with X-Gene SoC that represents the "world's first ARMv8 64-bit server on a chip solution." 64-bit ARM hardware has begun sampling to ARM Linux stakeholders in very limited quantities. He unfortunately is unable to share any early performance figures or much information on the APM Mustang hardware, but he did share today that 64-bit ARM support for Firefox is working.
A few months ago Marcin Juszkiewicz worked on upstream Xulrunner AArch64 support along with code for some related projects so they would be ready for the 64-bit ARM world and that work can now be realized. Marcin has tested Firefox on the APM Mustang ARMv8 hardware with YouTube, complete with HTML5 video playback. The AArch64 packages were from Fedora Rawhide and using X11 forwarding to his desktop from the 64-bit ARM server.
More information can be found from Marcin's blog post.