From ff2e0c8afd5e9b3b43267409b5bbce63bcddccea Mon Sep 17 00:00:00 2001
From: Jonas Jenwald <jonas.jenwald@gmail.com>
Date: Thu, 18 Apr 2024 12:39:57 +0200
Subject: [PATCH] Skip the scroll/scrollend workaround in the Firefox PDF
 Viewer (PR 17724 follow-up)

Given that [bug 1881974](https://bugzilla.mozilla.org/show_bug.cgi?id=1881974) has been fixed in Firefox 126, the workaround should no longer be necessary in the *built-in* Firefox PDF Viewer.
---
 web/app.js | 31 +++++++++++++++++++------------
 1 file changed, 19 insertions(+), 12 deletions(-)

diff --git a/web/app.js b/web/app.js
index cda101c7c..f288c2adf 100644
--- a/web/app.js
+++ b/web/app.js
@@ -177,8 +177,6 @@ const PDFViewerApplication = {
   _nimbusDataPromise: null,
   _caretBrowsing: null,
   _isScrolling: false,
-  _lastScrollTop: 0,
-  _lastScrollLeft: 0,
 
   // Called once when the document is loaded.
   async initialize(appConfig) {
@@ -2002,15 +2000,20 @@ const PDFViewerApplication = {
     ) {
       return;
     }
-
-    // Using the values lastScrollTop and lastScrollLeft is a workaround to
-    // https://bugzilla.mozilla.org/show_bug.cgi?id=1881974.
-    // TODO: remove them once the bug is fixed.
-    ({ scrollTop: this._lastScrollTop, scrollLeft: this._lastScrollLeft } =
-      mainContainer);
-    const scrollend = () => {
+    if (typeof PDFJSDev === "undefined" || !PDFJSDev.test("MOZCENTRAL")) {
+      // Using the values lastScrollTop and lastScrollLeft is a workaround to
+      // https://bugzilla.mozilla.org/show_bug.cgi?id=1881974.
+      // TODO: remove them once the bug is fixed.
       ({ scrollTop: this._lastScrollTop, scrollLeft: this._lastScrollLeft } =
         mainContainer);
+    }
+
+    const scrollend = () => {
+      if (typeof PDFJSDev === "undefined" || !PDFJSDev.test("MOZCENTRAL")) {
+        ({ scrollTop: this._lastScrollTop, scrollLeft: this._lastScrollLeft } =
+          mainContainer);
+      }
+
       this._isScrolling = false;
       mainContainer.addEventListener("scroll", scroll, {
         passive: true,
@@ -2020,13 +2023,17 @@ const PDFViewerApplication = {
       mainContainer.removeEventListener("blur", scrollend, { signal });
     };
     const scroll = () => {
+      if (this._isCtrlKeyDown) {
+        return;
+      }
       if (
-        this._isCtrlKeyDown ||
-        (this._lastScrollTop === mainContainer.scrollTop &&
-          this._lastScrollLeft === mainContainer.scrollLeft)
+        (typeof PDFJSDev === "undefined" || !PDFJSDev.test("MOZCENTRAL")) &&
+        this._lastScrollTop === mainContainer.scrollTop &&
+        this._lastScrollLeft === mainContainer.scrollLeft
       ) {
         return;
       }
+
       mainContainer.removeEventListener("scroll", scroll, {
         passive: true,
         signal,