Focus pdf-reader on tab selection if not focused contextPane note editor

chrome/content/zotero/bindings/noteeditor.xml

@@ -341,6 +341,7 @@
 
 		<content>
 			<xul:vbox xbl:inherits="flex" style="display: flex;flex-direction: column;flex-grow: 1;">
+				<!-- Notice: Update query selector for `iframe[anonid="editor-view"]` in contextPane.js if updating this -->
 				<xul:iframe tooltip="editor-tooltip" anonid="editor-view" flex="1" overflow="auto" style="width: 100%;margin-right: 5px;border: 0;width: 100%;margin-right: 5px;border: 0;flex-grow: 1;"
 							frameBorder="0" src="resource://zotero/note-editor/editor.html" type="content"/>
 				<xul:hbox id="links-container" hidden="true">

chrome/content/zotero/contextPane.js

@@ -170,6 +170,12 @@ var ZoteroContextPane = new function () {
 						(async () => {
 							await reader._initPromise;
 							_tabCover.hidden = true;
+							// Focus reader pages view if context pane note editor is not selected
+							if (Zotero_Tabs.selectedID == reader.tabID
+								&& (!document.activeElement
+									|| !document.activeElement.closest('.context-node iframe[anonid="editor-view"]'))) {
+								reader.focus();
+							}
 						})();
 
 						var attachment = Zotero.Items.get(reader.itemID);

chrome/content/zotero/xpcom/reader.js

@@ -40,6 +40,14 @@ class ReaderInstance {
 		});
 	}
 
+	focus() {
+		try {
+			this._iframeWindow.document.querySelector('#viewerContainer').focus();
+		}
+		catch (e) {
+		}
+	}
+
 	async open({ itemID, state, location }) {
 		let item = await Zotero.Items.getAsync(itemID);
 		if (!item) {