chore: Try Headless Firefox

[nschonni]

Trying the config from https://docs.travis-ci.com/user/gui-and-headless-browsers/#using-the-firefox-addon-in-headless-mode
Probably don't need "latest", but 60.0.2 is behind the latest ESR now, and is also about to bump https://www.mozilla.org/en-US/firefox/organizations/
Edit: Looks like this probably overlaps with

aria-practices/test/index.js

Line 11 in ecdb87a

const firefoxArgs = process.env.CI ? [ '-headless' ] : [];

[nschonni]

@spectranaut do you think there is value in adding jobs to test in Chrome and Safari?

[spectranaut]

I do think there is value in testing Chrome and Safari -- we could catch browser bugs :) Browsers aren't perfect and we don't know what browser people will be looking at the example from.

[nschonni]

Sounds good. I spun up the issue for now, but maybe i'll wait till your other improvements are in before sending a PR (if you don't beat me to it)

[nschonni]

@spectranaut looks like it sped up the runs a little bit, but since it didn't run the regression checks, maybe I should touch something so that the tests are run

[spectranaut]

Sorry this fell by the wayside for so long, @nschonni -- but you are right, the CI already runs headless filefox from the line you quoted. Just double checked I didn't invent the "CI" env variable: travis docs.

We should probably set firefox to latest. I'll just close this and open a new PR since I'm here :)