C.<p>Posting in case this helps someone else.</p><p>For the last month or two, I've had problems visiting some sites with <a href="https://mindly.social/tags/Firefox" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>Firefox</span></a>. The sites use <a href="https://mindly.social/tags/Cloudflare" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>Cloudflare</span></a>, and it would give the "prove you're a human by checking this box" prompt. I'd never had problems with this before.</p><p>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.</p><p>Based on a comment on this discussion:<br><a href="https://ask.metafilter.com/385480/fixing-Verify-You-Are-A-Human-Firefox-cookies-UBlock-Origin" rel="nofollow noopener noreferrer" translate="no" target="_blank"><span class="invisible">https://</span><span class="ellipsis">ask.metafilter.com/385480/fixi</span><span class="invisible">ng-Verify-You-Are-A-Human-Firefox-cookies-UBlock-Origin</span></a></p><p>... I tried disabling the "Disable HTML5 Autoplay" extension, and ... fixed! That was *not* an obvious candidate for causing the problem, unlike adblockers etc.</p><p>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.</p><p>Anyways, I hope this helps someone.</p><p><a href="https://mindly.social/tags/browser" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>browser</span></a> <a href="https://mindly.social/tags/check" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>check</span></a> <a href="https://mindly.social/tags/BrowserCheck" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>BrowserCheck</span></a> <a href="https://mindly.social/tags/human" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>human</span></a> <a href="https://mindly.social/tags/robot" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>robot</span></a> <a href="https://mindly.social/tags/ProveYoureHuman" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>ProveYoureHuman</span></a> <a href="https://mindly.social/tags/AreYouHuman" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>AreYouHuman</span></a> <a href="https://mindly.social/tags/fail" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>fail</span></a> <a href="https://mindly.social/tags/blocked" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>blocked</span></a> <a href="https://mindly.social/tags/website" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>website</span></a> <a href="https://mindly.social/tags/protection" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>protection</span></a> <a href="https://mindly.social/tags/HTML5" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>HTML5</span></a> <a href="https://mindly.social/tags/autoplay" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>autoplay</span></a> <a href="https://mindly.social/tags/extension" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>extension</span></a> <a href="https://mindly.social/tags/BrowserExtension" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>BrowserExtension</span></a></p>