Add ability to test on Firefox using selenium

📌 Use selenium/standalone-chrome instead of our chromedriver image Needs work has landed

Seems some work still going on in 📌 Use selenium/standalone-chrome instead of our chromedriver image Needs work

@smustgrave that's backports

MR appears to need rebase and has test failures too

@smustgrave yeah I'm waiting on upstream changes - this is all in the issue summary. The changes necessary to make tests on firefox can stll be reviewed. Hence the issue status.

We're green on firefox and chrome with no hacks to the codebase. Upstream fixes have been merged - thanks @justafish and @longwave.

This is now very ready for review.

Quickly skimmed and it's mostly test changes, and new Todo needs issue

I think the @todo's should be decided here - they are really about the issue - i.e should be testing things that seem untestable on firefox - or am I wrong and what we have here is a detectable firefox bug... for example is text just not appearing in firefox even though it is in chrome.