Add support for Firefox

[karlcow]

this is a followup on webcompat/web-bugs#32764 (comment)

Currently roll-call doesn't support firefox through user agent sniffing. But when we are faking the chrome ua on firefox, everything is working.

roll-call/index.js

Lines 10 to 14 in b9aab14

	const getChromeVersion = (force) => {
	if (force) return true
	var raw = navigator.userAgent.match(/Chrom(e|ium)\/([0-9]+)\./)
	return raw ? parseInt(raw[2], 10) > 59 : false
	}

roll-call/index.js

Lines 64 to 89 in b9aab14

	window.addEventListener('WebComponentsReady', () => {
	let url = new URL(window.location)
	let room = url.searchParams.get('room')
	let force = url.searchParams.get('force')
	if (window.location.search && getChromeVersion(force) && room) {
	require('./components')
	container.innerHTML = `${help}<roll-call call="${room}"></roll-call>`
	dragDrop('body', files => {
	document.querySelector('roll-call').serveFiles(files)
	})
	} else {
	container.innerHTML = welcome
	if (!getChromeVersion(force)) {
	document.querySelector('span.start-text').innerHTML = onlyChrome
	}
	each(document.querySelectorAll('welcome-message span'), elem => {
	elem.onclick = () => {
	let room
	if (elem.id === 'start-party') room = 'party'
	else room = random()
	window.location = window.location.pathname + '?room=' + room
	}
	})
	}
	})

these two blocks of code have to be modified.

A pr is welcome for this so the product is based on feature detection instead of user agent sniffing.