Use headlessFirefox and update to Node 20

[AA-Turner]

I had a very old branch (AA-Turner@3409085 // https://github.com/AA-Turner/sphinx/commits/use-jasmine/), most of which @jayaddison covered in the recent #12754. This PR takes a few ideas from that branch, such as avoiding xvfb-run as we don't need it, and also updates to the latest node LTS.

A

[jayaddison]

Thanks for the mention @AA-Turner - one question: when I search for nodejs in the Ubuntu package directory I find that Ubuntu noble is listed as LTS, and currently distributes NodeJS 18.19.1+dfsg-6ubuntu5. v18 also seems to be Node's current LTS distribution (codename hydrogen, v18.20.4).

Long story short: should we prefer v18 here instead of v20? (and/or maybe make it env.node-version-configurable again?)

[AA-Turner]

The website lists 20 as the latest LTS, as does endoflife.date. Version 18 is security-only.

configurable again

I didn't change env.node-version, I only increased the version number.

A

[jayaddison]

Ok, yep - my mistake; I'd checked the NodeJS readme, but not their website. Filed a small bugreport at nodejs/node#54419 to hopefully clear that up.