Script runs slow on Firefox using NVDA on windows 10

I noticed that the script runs really slowly and locks the page when using Firefox on Windows 10 along with NVDA.  Is this something that can be worked around?  I would assume this would be a common browser/screen reader combination.

Firefox 59.0.2
NVDA 2018.1.1

Page tested: http://n12v.com/focus-transition/