Add smooth scroll preference for tab startup and adjust visibility logic

src/browser/app/profile/zen-browser.js

@@ -181,6 +181,9 @@ pref('zen.splitView.min-resize-width', 7);
 pref('zen.splitView.change-on-hover', false);
 pref('zen.splitView.rearrange-hover-size', 24);
 
+// Startup flags
+pref('zen.startup.smooth-scroll-in-tabs', true);
+
 // Zen Workspaces
 pref('zen.workspaces.enabled', true);
 pref('zen.workspaces.hide-deactivated-workspaces', false);

src/browser/base/content/ZenStartup.mjs

@@ -34,7 +34,7 @@
         }
 
         // Disable smooth scroll
-        gBrowser.tabContainer.arrowScrollbox.smoothScroll = false;
+        gBrowser.tabContainer.arrowScrollbox.smoothScroll = Services.prefs.getBoolPref('zen.startup.smooth-scroll-in-tabs', false);
 
         ZenWorkspaces.init();
         gZenUIManager.init();

src/browser/components/tabbrowser/content/tabs-js.patch

@@ -1,5 +1,5 @@
 diff --git a/browser/components/tabbrowser/content/tabs.js b/browser/components/tabbrowser/content/tabs.js
-index f7c39fe804182e2bdf53045ba3b6a5ba17079fc3..93be23da305a5e2e51bff1c5b5f287439a8fafa8 100644
+index f7c39fe804182e2bdf53045ba3b6a5ba17079fc3..bddba0cb7b475ca7a8d0e58227c62f82b62e118b 100644
 --- a/browser/components/tabbrowser/content/tabs.js
 +++ b/browser/components/tabbrowser/content/tabs.js
 @@ -649,7 +649,7 @@
@@ -158,3 +158,73 @@ index f7c39fe804182e2bdf53045ba3b6a5ba17079fc3..93be23da305a5e2e51bff1c5b5f28743
          return;
        }
  
+@@ -2726,12 +2730,14 @@
+               selectedTab = {
+                 left: selectedTab.left,
+                 right: selectedTab.right,
++                top: selectedTab.top,
++                bottom: selectedTab.bottom
+               };
+             }
+             return [
+               this._lastTabToScrollIntoView,
+               this.arrowScrollbox.scrollClientRect,
+-              { left: lastTabRect.left, right: lastTabRect.right },
++              lastTabRect,
+               selectedTab,
+             ];
+           })
+@@ -2748,8 +2754,13 @@
+             delete this._lastTabToScrollIntoView;
+             // Is the new tab already completely visible?
+             if (
+-              scrollRect.left <= tabRect.left &&
+-              tabRect.right <= scrollRect.right
++              this.verticalMode ? (
++                scrollRect.top <= tabRect.top &&
++                tabRect.bottom <= scrollRect.bottom
++              ) : (
++                scrollRect.left <= tabRect.left &&
++                tabRect.right <= scrollRect.right
++              )
+             ) {
+               return;
+             }
+@@ -2758,19 +2769,30 @@
+               // Can we make both the new tab and the selected tab completely visible?
+               if (
+                 !selectedRect ||
+-                Math.max(
+-                  tabRect.right - selectedRect.left,
+-                  selectedRect.right - tabRect.left
+-                ) <= scrollRect.width
++                this.verticalMode ? (
++                  Math.max(
++                    tabRect.bottom - selectedRect.top,
++                    selectedRect.bottom - tabRect.top
++                  ) <= scrollRect.height
++                ) : (
++                  Math.max(
++                    tabRect.right - selectedRect.left,
++                    selectedRect.right - tabRect.left
++                  ) <= scrollRect.width
++                )
+               ) {
+                 this.arrowScrollbox.ensureElementIsVisible(tabToScrollIntoView);
+                 return;
+               }
+ 
+               this.arrowScrollbox.scrollByPixels(
+-                this.#rtlMode
+-                  ? selectedRect.right - scrollRect.right
+-                  : selectedRect.left - scrollRect.left
++                this.verticalMode ? (
++                  tabRect.top - selectedRect.top
++                ) : (
++                  this.#rtlMode
++                    ? selectedRect.right - scrollRect.right
++                    : selectedRect.left - scrollRect.left
++                )
+               );
+             }
+