Add error handling to tab animation and refine empty tab selection logic

src/browser/base/content/ZenUIManager.mjs

@@ -347,6 +347,7 @@ var gZenVerticalTabsManager = {
       return visibleTabs[visibleTabs.length - 1] === aTab;
     };
 
+    try {
       const tabSize = aTab.getBoundingClientRect().height;
       const transform = `-${tabSize}px`;
       gZenUIManager.motion
@@ -374,6 +375,9 @@ var gZenVerticalTabsManager = {
         .then(() => {
           aTab.querySelector('.tab-stack').style.removeProperty('filter');
         });
+    } catch (e) {
+      console.error(e);
+    }
   },
 
   get actualWindowButtons() {

src/browser/base/zen-components/ZenWorkspaces.mjs

@@ -628,7 +628,7 @@ var ZenWorkspaces = new (class extends ZenMultiWindowFeature {
         (currentTab.isEmpty &&
           (currentTab.getAttribute('image') === gPageIcons[currentTabURL] || !currentTab.hasAttribute('image'))) ||
         currentTab.hasAttribute('zen-empty-tab') ||
-        currentTab._possibleEmptyTab
+        (currentTab._possibleEmptyTab && currentTab.isEmpty)
       ) {
         this.selectEmptyTab();
         this._removedByStartupPage = true;