MacBook 2014-ish w/ OSX-Safari betas::
Nice first impression . . . . After a bit the controls become non-responsive.
Unclear as to the situation(s) where this happens.
The display does NOT freeze but continues to display and the cursor responds/moves but mode will not change. Reload page seems to fix.
Details very vague/hazy at this point.

( MacBookPro 11,1 / OSX 10.12.3 beta / Safari 10.0.3 )