useIframe completely fails in all mobile browsers, Safari on Mac on SauceLabs

### Expected behavior

it works
### Actual behavior

test disconnects. It seems that these browsers don't work with the option unless there are further options passed into the runner for each browser. However, there is no documentation of other options, either in karma, or anywhere on the web, so it appears that either karma needs to fix this or the documentation needs to state that it only works with chrome, IE, Edge, and firefox
### Enviroment Details

saucelabs
- Karma version (output of `karma --version`):
- Relevant part of your `karma.config.js` file
### Steps to reproduce the behaviour
1. client: { useIframes: false} in karma.conf.js
2. run any saucelabs browser test with Safari on Mac, or any mobile browser
3. watch it fail