Posting in case this helps someone else.
For the last month or two, I've had problems visiting some sites with #Firefox. The sites use #Cloudflare, and it would give the "prove you're a human by checking this box" prompt. I'd never had problems with this before.
Suddenly that started failing consistently. Clicking the box would do something, but then just reload the challenge. There was no way to pass it. I tried reconfiguring and even disabling the "uBlock Origin" extension, cookie policies, other things - no luck.
Based on a comment on this discussion:
https://ask.metafilter.com/385480/fixing-Verify-You-Are-A-Human-Firefox-cookies-UBlock-Origin
... I tried disabling the "Disable HTML5 Autoplay" extension, and ... fixed! That was *not* an obvious candidate for causing the problem, unlike adblockers etc.
So it appears Cloudflare changed their in-browser testing JS such that it requires HTML5 autoplay to pass the check. Which is ... special. I can think of lots of people with very good reasons to have that disabled.
Anyways, I hope this helps someone.
#browser #check #BrowserCheck #human #robot #ProveYoureHuman #AreYouHuman #fail #blocked #website #protection #HTML5 #autoplay #extension #BrowserExtension