Slowdowns and occasional freezes when using Safari 13 on MacOS 10.14.6

[loganbraywork]

Test device
Jordan
Operating System
10.14.6
Browser
13.0
Problem description
From phetsims/qa#425

Extreme slowdowns when switching to and from full-screen mode on MacOS 10.14.6. Sometimes causes freezes and the occasional crash. Most frequently occurs when screen is maximized.
Steps to reproduce

1. Maximize browser window
2. Check Energy Symbols and Link Heaters boxes
3. Boil water using Heat slider
4. Enter and exit full-screen

Troubleshooting information:
!!!!! DO NOT EDIT !!!!!
Name: ‫تست (زبان)‬
URL: https://phet-dev.colorado.edu/html/energy-forms-and-changes/1.2.0-rc.1/phet/energy-forms-and-changes_all_phet.html?stringTest=rtl
Version: 1.2.0-rc.1 2019-09-06 15:16:27 UTC
Features missing: touch
User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_6) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/13.0 Safari/605.1.15
Language: en-US
Window: 1366x705
Pixel Ratio: 1/1
WebGL: WebGL 1.0
GLSL: WebGL GLSL ES 1.0 (1.20)
Vendor: WebKit (WebKit WebGL)
Vertex: attribs: 16 varying: 15 uniform: 1024
Texture: size: 16384 imageUnits: 16 (vertex: 16, combined: 16)
Max viewport: 8192x8192
OES_texture_float: true
Dependencies JSON: {}