The page is placing an abspolute-positioned `input type="radio"` element wayyyy off to the side in a scrollable container (with `right:9999px`), and they're giving it zero height and width, which Chrome honors but Firefox does not (we floor the size to 4px). Since we've got it as having a nonzero size, it actually contributes to the scrollable overflow for us, which means we would generate scrollbars if this element were `overflow:auto` (in fact it's `overflow:hidden`, but we effectively generate logical/invisible scrollbars to let it be programmatically scrolled-to). And when it becomes checked, we scroll to show it -- it's the tiny dot that was mentioned in comment 0 actual-results). In comparison: in Chrome, the zero-sized radio button is actually zero-sized and hence doesn't contribute scrollable overflow, and hence it can't be scrolled to when its label is clicked. If I open Chrome devtools to force `width:4px; height:4px` on the radio button (to match Firefox's lower bound), **then** Chrome matches Firefox exactly on this site.
Bug 1900326 Comment 6 Edit History
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The page is placing an absolute-positioned `input type="radio"` element wayyyy off to the side in a scrollable container (with `right:9999px`), and they're giving it zero height and width, which Chrome honors but Firefox does not (we floor the size to 4px). Since we've got it as having a nonzero size, it actually contributes to the scrollable overflow for us, which means we would generate scrollbars if this element were `overflow:auto` (in fact it's `overflow:hidden`, but we effectively generate logical/invisible scrollbars to let it be programmatically scrolled-to). And when it becomes checked, we scroll to show it -- it's the tiny dot that was mentioned in comment 0 actual-results). In comparison: in Chrome, the zero-sized radio button is actually zero-sized and hence doesn't contribute scrollable overflow, and hence it can't be scrolled to when its label is clicked. If I open Chrome devtools to force `width:4px; height:4px` on the radio button (to match Firefox's lower bound), **then** Chrome matches Firefox exactly on this site.