Could someone confirm? The test page is here (Safari and Chrome behave correctly):
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iOS Firefox uses the same engine as Safari. Anyway, how should the test behave?
When scrolling the page to hide Firefox’s address bar, the svh bar should remain small (smaller than the height of the page). When scrolling back up to show the address bar again, the vh and lvh bars should remain large and become cut off on the bottom.
You seem to be correct. Additionally, it seems to not be handled properly in the in-app browser.
EDIT: Strike that second part. It’s just very confusing.
I found the Firefox iOS bug: