diff --git a/chrome/content/zotero/xpcom/zotero.js b/chrome/content/zotero/xpcom/zotero.js
index 7bbeb0a692..dc0039528e 100644
--- a/chrome/content/zotero/xpcom/zotero.js
+++ b/chrome/content/zotero/xpcom/zotero.js
@@ -205,6 +205,8 @@ const { CommandLineOptions } = ChromeUtils.importESModule("chrome://zotero/conte
 		this.uiReadyPromise.then(() => {
 			Zotero.debug("User interface ready in " + (new Date() - _startupTime) + " ms");
 		});
+		this.startupSyncDeferred = Zotero.Promise.defer();
+		this.startupSyncPromise = this.startupSyncDeferred.promise;
 		
 		if (options) {
 			let opts = [
diff --git a/chrome/content/zotero/zoteroPane.js b/chrome/content/zotero/zoteroPane.js
index 54d8c11511..0a59c7b583 100644
--- a/chrome/content/zotero/zoteroPane.js
+++ b/chrome/content/zotero/zoteroPane.js
@@ -862,6 +862,7 @@ var ZoteroPane = new function () {
 		}
 		
 		// Auto-sync on pane open or if new account
+		let startupSync = false;
 		if (Zotero.Prefs.get('sync.autoSync') || Zotero.initAutoSync) {
 			await Zotero.proxyAuthComplete;
 			await Zotero.uiReadyPromise;
@@ -879,11 +880,19 @@ var ZoteroPane = new function () {
 				Zotero.debug('Firefox profile access error -- skipping initial auto-sync', 4);
 			}
 			else {
+				startupSync = true;
 				Zotero.Sync.Runner.sync({
 					background: true
-				}).then(() => Zotero.initAutoSync = false);
+				})
+				.then(() => {
+					Zotero.initAutoSync = false;
+					Zotero.startupSyncDeferred.resolve();
+				});
 			}
 		}
+		if (!startupSync) {
+			Zotero.startupSyncDeferred.resolve();
+		}
 		
 		// Set sync icon to spinning if there's an existing sync
 		//