To repro:

1. Visit phishing.safebrowsingtest.com or https://aws1.mdw.la/fw to get an interstitial
2. Use a screen reader and explore the page linearly one element at a time
3. The "details" section should be hidden from the accessibility tree when it's invisible on the screen.

Solution: when the item has class="hidden", add aria-hidden="true" to it also. That will allow you to leave it in the DOM so it can animate but keep it hidden from accessibility when it's effectively hidden.

Originally noticed on Android, but the code appears to be the same on almost all platforms:

components/security_interstitials/core/browser/resources/interstitial_v2.*