Refactor welcome page transitions and reorganize tabs after welcome screen

src/browser/base/content/zen-styles/zen-welcome.css

@@ -167,6 +167,9 @@
       width: 1px;
       height: 1px;
       margin: 8rem auto auto 13.4rem;
+      @media (-moz-platform: macos) {
+        margin: 4rem auto auto 10.5rem;
+      }
     }
 
     #zen-welcome-initial-essentials-browser {

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

@@ -177,7 +177,14 @@
     async next() {
       if (this._currentPage !== -1) {
         const previousPage = this._pages[this._currentPage];
-        await Promise.all([this.fadeOutTitles(), this.fadeOutButtons(), this.fadeOutContent()]);
+        const promises = [
+          this.fadeOutTitles(),
+          this.fadeOutButtons(),
+        ];
+        if (!previousPage.dontFadeOut) {
+          promises.push(this.fadeOutContent());
+        }
+        await Promise.all(promises);
         await previousPage.fadeOut();
         document.getElementById('zen-welcome-page-content').innerHTML = '';
       }
@@ -193,6 +200,7 @@
     }
 
     async finish() {
+      ZenWorkspaces.reorganizeTabsAfterWelcome();
       await animate('#zen-welcome-page-content', { x: [0, '100%'] }, { bounce: 0 });
       document.getElementById('zen-welcome-page-content').remove();
       await this.animHeart();
@@ -319,6 +327,7 @@
             position: 'top',
           });
         },
+        dontFadeOut: true,
         async fadeOut() {
           gZenThemePicker.panel.removeAttribute('noautohide');
           gZenThemePicker.panel.removeAttribute('consumeoutsideclicks');

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

@@ -2229,4 +2229,12 @@ var ZenWorkspaces = new (class extends ZenMultiWindowFeature {
       (tab) => tab.hasAttribute('zen-essential') || tab.getAttribute('zen-workspace-id') === currentWorkspace
     );
   }
+
+  reorganizeTabsAfterWelcome() {
+    const children = gBrowser.tabContainer.arrowScrollbox.children;
+    const remainingTabs = Array.from(children).filter((child) => child.tagName === 'tab');
+    for (const tab of remainingTabs) {
+      this.moveTabToWorkspace(tab, this.activeWorkspace);
+    }
+  }
 })();