wait for scroll controller attachment

app/lib/features/geckoview/features/browser/presentation/widgets/sheets/view_tabs.dart

@@ -346,7 +346,14 @@ class ViewTabsSheetWidget extends HookConsumerWidget {
                   );
 
                   final lastScroll = useRef<String?>(null);
-                  useEffect(() {
+                  final scrollControllerIsAttached = useListenableSelector(
+                    sheetScrollController,
+                    () => sheetScrollController.hasClients,
+                  );
+
+                  useEffect(
+                    () {
+                      if (scrollControllerIsAttached) {
                         if (lastScroll.value != activeTab) {
                           final index = filteredTabEntities.value.indexWhere(
                             (entity) => entity.tabId == activeTab,
@@ -368,9 +375,16 @@ class ViewTabsSheetWidget extends HookConsumerWidget {
                             }
                           }
                         }
+                      }
 
                       return null;
-                  }, [filteredTabEntities, activeTab]);
+                    },
+                    [
+                      filteredTabEntities,
+                      activeTab,
+                      scrollControllerIsAttached,
+                    ],
+                  );
 
                   final tabs = useMemoized(() {
                     return filteredTabEntities.value
@@ -391,7 +405,7 @@ class ViewTabsSheetWidget extends HookConsumerWidget {
                   return Padding(
                     padding: const EdgeInsets.symmetric(horizontal: 4.0),
                     child: FadingScroll(
-                      fadingSize: 10,
+                      fadingSize: 5,
                       controller: sheetScrollController,
                       builder: (context, controller) {
                         return ReorderableBuilder.builder(