Implement tab duplication

Fixes #2566

chrome/content/zotero/tabs.js

@@ -319,7 +319,8 @@ var Zotero_Tabs = new function () {
 			this.close(tab.id);
 			Zotero.Reader.open(tab.data.itemID, null, {
 				title: tab.title,
-				tabIndex
+				tabIndex,
+				allowDuplicate: true
 			});
 			return;
 		}
@@ -485,6 +486,18 @@ var Zotero_Tabs = new function () {
 				}
 			});
 			menupopup.appendChild(menuitem);
+			// Duplicate tab
+			menuitem = document.createElement('menuitem');
+			menuitem.setAttribute('label', Zotero.getString('tabs.duplicate'));
+			menuitem.addEventListener('command', () => {
+				var { tab, tabIndex } = this._getTab(id);
+				if (tab.data.itemID) {
+					tabIndex++;
+					Zotero.Reader.open(tab.data.itemID, null, { tabIndex, allowDuplicate: true });
+
+				}
+			});
+			popup.appendChild(menuitem);
 			// Separator
 			popup.appendChild(document.createElement('menuseparator'));
 		}

chrome/content/zotero/xpcom/reader.js

@@ -1270,7 +1270,7 @@ class Reader {
 		await this.open(item.id, location, options);
 	}
 
-	async open(itemID, location, { title, tabIndex, openInBackground, openInWindow } = {}) {
+	async open(itemID, location, { title, tabIndex, openInBackground, openInWindow, allowDuplicate } = {}) {
 		this._loadSidebarState();
 		this.triggerAnnotationsImportCheck(itemID);
 		let reader;
@@ -1278,7 +1278,7 @@ class Reader {
 		if (openInWindow) {
 			reader = this._readers.find(r => r._itemID === itemID && (r instanceof ReaderWindow));
 		}
-		else {
+		else if (!allowDuplicate) {
 			reader = this._readers.find(r => r._itemID === itemID);
 		}
 

chrome/locale/en-US/zotero/zotero.properties

@@ -1404,5 +1404,6 @@ tabs.move = Move Tab
 tabs.moveToStart = Move to Start
 tabs.moveToEnd = Move to End
 tabs.moveToWindow = Move to New Window
+tabs.duplicate = Duplicate Tab
 tabs.undoClose = Reopen Closed Tab;Reopen Closed Tabs
 tabs.closeOther = Close Other Tabs