Each window has its own URL bar — type a URL and hit Enter or click ↻. Reload All pushes the top-bar URL to all non-frozen windows. ⏸ freezes a window so it's left untouched.
Site loads blank? It blocks embedding (X-Frame-Options) — flip Proxy: on to load it through a header-stripping proxy (layout preview; sites needing login or heavy same-origin JS may still not work).
📏 Ruler measures in real device pixels — drag across any frame and it divides by that frame's scale. Esc exits. (While on, it covers the frames; toggle off to scroll inside one.)