Who has two thumbs and just wasted two and a half hours of his Saturday morning failing to connect to his instance of #homeassistant but only in firefox, not in chrome or safari?
Yup, this guy, who has the unfortunate combination of uBlock Origin, EasyList blocklist, and duckdns for his dynamic DNS.
Once I worked out that EasyList is blocking websockets to duckdns, it was easy enough to add a whitelist for my own hostname, but urgh, very annoying.

I was trying to find out when it was changed (I suspect in the last 12 hours, as this was working last night), but github is showing me unicorns instead of git blame for that particular file, and as I've fixed it, I don't care enough to dig more ;-)