diff --git a/extensions/chromium/preferences_schema.json b/extensions/chromium/preferences_schema.json
index 7c00e57e6ba1d..476e1b368ba07 100644
--- a/extensions/chromium/preferences_schema.json
+++ b/extensions/chromium/preferences_schema.json
@@ -198,6 +198,10 @@
       "description": "The color is a string as defined in CSS. Its goal is to help improve readability in high contrast mode",
       "type": "string",
       "default": "CanvasText"
+    },
+    "hasInitializationHook": {
+      "type": "boolean",
+      "default": false
     }
   }
 }
diff --git a/test/integration/copy_paste_spec.mjs b/test/integration/copy_paste_spec.mjs
index dac86b8cf11dd..35f27a1bcda90 100644
--- a/test/integration/copy_paste_spec.mjs
+++ b/test/integration/copy_paste_spec.mjs
@@ -14,6 +14,7 @@
  */
 
 import {
+  awaitPromise,
   closePages,
   kbCopy,
   kbSelectAll,
@@ -44,12 +45,7 @@ describe("Copy and paste", () => {
         "tracemonkey.pdf",
         "#hiddenCopyElement",
         100,
-        async page => {
-          await page.waitForFunction(
-            () => !!window.PDFViewerApplication.eventBus
-          );
-          await waitForTextLayer(page);
-        }
+        waitForTextLayer
       );
       await mockClipboard(pages);
     });
@@ -60,7 +56,8 @@ describe("Copy and paste", () => {
 
     it("must check that we've all the contents on copy/paste", async () => {
       await Promise.all(
-        pages.map(async ([browserName, page]) => {
+        pages.map(async ([browserName, page, pageSetupPromise]) => {
+          awaitPromise(pageSetupPromise);
           await selectAll(page);
 
           const promise = waitForEvent(page, "copy");
@@ -151,12 +148,7 @@ describe("Copy and paste", () => {
         "copy_paste_ligatures.pdf",
         "#hiddenCopyElement",
         100,
-        async page => {
-          await page.waitForFunction(
-            () => !!window.PDFViewerApplication.eventBus
-          );
-          await waitForTextLayer(page);
-        }
+        waitForTextLayer
       );
       await mockClipboard(pages);
     });
@@ -167,7 +159,8 @@ describe("Copy and paste", () => {
 
     it("must check that the ligatures have been removed when the text has been copied", async () => {
       await Promise.all(
-        pages.map(async ([browserName, page]) => {
+        pages.map(async ([browserName, page, pageSetupPromise]) => {
+          awaitPromise(pageSetupPromise);
           await selectAll(page);
 
           const promise = waitForEvent(page, "copy");
diff --git a/test/integration/freetext_editor_spec.mjs b/test/integration/freetext_editor_spec.mjs
index f3cff4cea8164..a09994233824a 100644
--- a/test/integration/freetext_editor_spec.mjs
+++ b/test/integration/freetext_editor_spec.mjs
@@ -2216,20 +2216,14 @@ describe("FreeText Editor", () => {
         "tracemonkey.pdf",
         ".annotationEditorLayer",
         100,
-        async page => {
-          await page.waitForFunction(async () => {
-            await window.PDFViewerApplication.initializedPromise;
-            return true;
-          });
-          await page.evaluate(() => {
-            window.visitedPages = [];
-            window.PDFViewerApplication.eventBus.on(
-              "pagechanging",
-              ({ pageNumber }) => {
-                window.visitedPages.push(pageNumber);
-              }
-            );
-          });
+        () => {
+          window.visitedPages = [];
+          window.PDFViewerApplication.eventBus.on(
+            "pagechanging",
+            ({ pageNumber }) => {
+              window.visitedPages.push(pageNumber);
+            }
+          );
         }
       );
     });
@@ -2469,19 +2463,13 @@ describe("FreeText Editor", () => {
         "tracemonkey.pdf",
         ".annotationEditorLayer",
         100,
-        async page => {
-          await page.waitForFunction(async () => {
-            await window.PDFViewerApplication.initializedPromise;
-            return true;
-          });
-          await page.evaluate(() => {
-            window.PDFViewerApplication.eventBus.on(
-              "annotationeditorstateschanged",
-              ({ details }) => {
-                window.editingEvents?.push(details);
-              }
-            );
-          });
+        () => {
+          window.PDFViewerApplication.eventBus.on(
+            "annotationeditorstateschanged",
+            ({ details }) => {
+              window.editingEvents?.push(details);
+            }
+          );
         }
       );
     });
diff --git a/test/integration/scripting_spec.mjs b/test/integration/scripting_spec.mjs
index 5f29be1ef4547..b6bf98c10597f 100644
--- a/test/integration/scripting_spec.mjs
+++ b/test/integration/scripting_spec.mjs
@@ -1773,7 +1773,6 @@ describe("Interaction", () => {
 
   describe("in autoprint.pdf", () => {
     let pages;
-    const printHandles = new Map();
 
     beforeAll(async () => {
       // Autoprinting is triggered by the `Open` event, which is one of the
@@ -1788,29 +1787,9 @@ describe("Interaction", () => {
         "autoprint.pdf",
         "",
         null /* pageSetup = */,
-        async page => {
-          printHandles.set(
-            page,
-            await page.evaluateHandle(() => [
-              new Promise(resolve => {
-                globalThis.printResolve = resolve;
-              }),
-            ])
-          );
-          await page.waitForFunction(() => {
-            if (!window.PDFViewerApplication?.eventBus) {
-              return false;
-            }
-            window.PDFViewerApplication.eventBus.on(
-              "print",
-              () => {
-                const resolve = globalThis.printResolve;
-                delete globalThis.printResolve;
-                resolve();
-              },
-              { once: true }
-            );
-            return true;
+        resolve => {
+          window.PDFViewerApplication.eventBus.on("print", resolve, {
+            once: true,
           });
         }
       );
@@ -1818,13 +1797,12 @@ describe("Interaction", () => {
 
     afterAll(async () => {
       await closePages(pages);
-      printHandles.clear();
     });
 
     it("must check if printing is triggered when the document is open", async () => {
       await Promise.all(
-        pages.map(async ([browserName, page]) => {
-          await awaitPromise(printHandles.get(page));
+        pages.map(async ([browserName, page, pageSetupPromise]) => {
+          await awaitPromise(pageSetupPromise);
         })
       );
     });
diff --git a/test/integration/test_utils.mjs b/test/integration/test_utils.mjs
index 037b547a1d7e5..9246117275a18 100644
--- a/test/integration/test_utils.mjs
+++ b/test/integration/test_utils.mjs
@@ -37,6 +37,10 @@ function loadAndWait(filename, selector, zoom, pageSetup, options) {
       });
 
       let app_options = "";
+      if (pageSetup) {
+        options ||= {};
+        options.initializationhook = "true";
+      }
       if (options) {
         // Options must be handled in app.js::_parseHashParams.
         for (const [key, value] of Object.entries(options)) {
@@ -48,8 +52,25 @@ function loadAndWait(filename, selector, zoom, pageSetup, options) {
       }?file=/test/pdfs/${filename}#zoom=${zoom ?? "page-fit"}${app_options}`;
 
       await page.goto(url);
+      let pageSetupPromise = null;
       if (pageSetup) {
-        await pageSetup(page);
+        await page.waitForFunction(
+          () => !!window.PDFViewerApplication.eventBus
+        );
+        pageSetupPromise = await page.evaluateHandle(
+          cb => [
+            new Promise(resolve => {
+              window.PDFViewerApplication.eventBus.dispatch(
+                "initializationhook",
+                {
+                  // eslint-disable-next-line no-eval
+                  callback: () => eval(`(${cb})`)(resolve),
+                }
+              );
+            }),
+          ],
+          pageSetup.toString()
+        );
       }
 
       await page.bringToFront();
@@ -58,7 +79,7 @@ function loadAndWait(filename, selector, zoom, pageSetup, options) {
           timeout: 0,
         });
       }
-      return [session.name, page];
+      return [session.name, page, pageSetupPromise];
     })
   );
 }
@@ -298,20 +319,15 @@ async function dragAndDropAnnotation(page, startX, startY, tX, tY) {
   await page.waitForSelector("#viewer:not(.noUserSelect)");
 }
 
-function waitForAnnotationEditorLayer(page) {
-  return createPromise(page, resolve => {
-    window.PDFViewerApplication.eventBus.on(
-      "annotationeditorlayerrendered",
-      resolve
-    );
-  });
+function waitForAnnotationEditorLayer(resolve) {
+  window.PDFViewerApplication.eventBus.on(
+    "annotationeditorlayerrendered",
+    resolve
+  );
 }
 
-async function waitForTextLayer(page) {
-  const handle = await createPromise(page, resolve => {
-    window.PDFViewerApplication.eventBus.on("textlayerrendered", resolve);
-  });
-  return awaitPromise(handle);
+function waitForTextLayer(resolve) {
+  window.PDFViewerApplication.eventBus.on("textlayerrendered", resolve);
 }
 
 async function scrollIntoView(page, selector) {
diff --git a/web/app.js b/web/app.js
index 49cf9a9f53faf..19b82fe28e810 100644
--- a/web/app.js
+++ b/web/app.js
@@ -237,6 +237,23 @@ const PDFViewerApplication = {
     this.bindEvents();
     this.bindWindowEvents();
 
+    if (
+      typeof PDFJSDev !== "undefined" &&
+      PDFJSDev.test("TESTING || MOZCENTRAL") &&
+      AppOptions.get("hasInitializationHook")
+    ) {
+      await new Promise(resolve => {
+        this.eventBus.on(
+          "initializationhook",
+          ({ callback }) => {
+            callback();
+            resolve();
+          },
+          { once: true }
+        );
+      });
+    }
+
     this._initializedCapability.resolve();
   },
 
@@ -329,6 +346,9 @@ const PDFViewerApplication = {
           params.get("highlighteditorcolors")
         );
       }
+      if (params.get("initializationhook") === "true") {
+        AppOptions.set("hasInitializationHook", true);
+      }
     }
   },
 
diff --git a/web/app_options.js b/web/app_options.js
index 80fdc9c24d647..61ad13862f93c 100644
--- a/web/app_options.js
+++ b/web/app_options.js
@@ -181,6 +181,11 @@ const defaultOptions = {
     value: 0,
     kind: OptionKind.VIEWER + OptionKind.PREFERENCE,
   },
+  hasInitializationHook: {
+    /** @type {boolean} */
+    value: false,
+    kind: OptionKind.VIEWER + OptionKind.PREFERENCE,
+  },
   highlightEditorColors: {
     /** @type {string} */
     value: "yellow=#FFFF98,green=#53FFBC,blue=#80EBFF,pink=#FFCBE6,red=#FF4F5F",