Split from https://gitlab.torproject.org/tpo/applications/tor-browser/-/issues/22137, which had a larger scope and stalled due to the "overlay" vs "non-overlay" decision. As summarised in https://gitlab.torproject.org/tpo/applications/tor-browser/-/issues/22137#note_2954880 windows 10 and windows 11 have different scollbar sizes, plus could leak a rare system setting. This issue is just interested in closing this one hole.