STR: 1. Load http://web.aceattorneyonline.com/ in Firefox mobile 2. Zoom in or out The fixed element on the right side of the screen appears to stay fixed to the visual viewport rather than the layout viewport.

We appear to be attaching the fixed element to what we compute as the layout viewport. Indeed, if you zoom in enough, the element stops being attached to the visual viewport (which means bug 656036 did improve the experience on this page to some extent). However, it appears we compute a smaller layout viewport than Chrome.

(In reply to Botond Ballo [:botond] from comment #1) > However, it appears we compute a smaller layout viewport than Chrome. To be more precise, this is one of the cases where Chrome's "fixed viewport" size is larger than the ICB size. We currently conflate these two concepts (referring to them both as the "layout viewport"), but that will be fixed in bug 1423013 (see in particular bug 1423013 comment 11), which should fix this site too.

The part of the fix has been moved into bug 1516377.