It just redirects everything to https://www.google.com/httpservice/retry/enablejs?sei=... I guess this is the inevitable end of the era of the web as a collection of hyperlinked documents and the beginning of the web as an application delivery protocol.
In other browsers with JS disabled google search still works but this computational paywall rollout for Firefox esr is a sign of things to come.
With the caveat that this used to 100% work, but since a couple months, it indeed occasionally redirects to the “Turn on JavaScript to keep searching” page you mention, https://www.google.com/httpservice/retry/enablejs . I'd say the refusal happens 1 / 20 searches. Said differently, I’d prefix your “refusing” with a “sometimes”.
I haven’t investigated the reason for this sometimes-ness. Would love to find an answer here, or ideas/leads (aside switching to another search engine, yes I do know about them, but sometimes Google remains better). Or maybe the sometimes-ness was just A/B testing, and the full switch is happening and this is now a thing of the past.
EDIT you must have posted precisely at the moment of the end of the A/B test: I did several non-JS searches today at $job, and to confirm what I was writing here I did a test one, successfully. But 30min later, I confirm your observation: 100% blocked.