>>825
Macにだけ行の高さ(24px)が設定されているみたい
https://dxr.mozilla.org/mozilla-central/rev/1a5b53a831e5/browser/themes/osx/places/places.css#25
これで狭められるんじゃないかな
@-moz-document url("chrome://browser/content/bookmarks/bookmarksPanel.xul"),
url("chrome://browser/content/history/history-panel.xul") {
.sidebar-placesTree,
.sidebar-placesTreechildren::-moz-tree-row {
height: auto !important;
}
}