Wow. this was a mission.
I'm on a Mac Sierra 10.12 with an ESP8266.
First, Arduino kept crashing.
Crash errors: nsinvalidargumentexception and setAutomaticCustomizeTouchBarMenuItemEnabled
It took probably 10 tries of installing different versions but Arduino keeps crashing
SOLUTION:
https://www.arduino.cc/download_handler.php?f=/arduino-1.8.7-macosx.zip
THEN I tried what felt like every SI Silicon Labs driver under the sun including the one that came with the manual to my ESP8266. DIDN't WORK. Tried quitting, restarting, updating java, different MicroUSB cables and followed this thread as well: #2
FINALLY here's the solution I found. The SI (cu.SLAB_USBtoUART) driver doesn't work, this one WORKS. Load it up.
SOLUTION:
http://blog.sengotta.net/wp-content/uploads/2015/11/CH341SER_MAC-1.4.zip