[Bug]: Integration tests with copyImage timeout in Firefox in headless mode #20918

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The issue is related to Integration test failures

Web browser and its version

firefox@nightly_150.0a1

Operating system and its version

macOS Tahoe Version 26.3.1

PDF.js version

v5.5.207

Is the bug present in the latest PDF.js version?

Yes

Is a browser extension

No

Steps to reproduce the problem

When running the integration tests locally in the headless mode on Firefox, all the integration tests using copyImage timeout with:

Error: Waiting for selector pdfjs_internal_editor_${N} canvas failed

I have a small reproduction for this:

import puppeteer from "puppeteer";
import fs from "fs";

const pngBase64 = fs.readFileSync("image.png").toString("base64");

const browser = await puppeteer.launch({
  headless: false,
  browser: "chrome",
});

const page = await browser.newPage();
await page.goto("https://example.com");

await page.evaluate(async (pngBase64) => {
  const res = await fetch(`data:image/png;base64,${pngBase64}`);
  const blob = await res.blob();
  await navigator.clipboard.write([new ClipboardItem({ "image/png": blob })]);
}, pngBase64);
console.log("write: ok");

await page.evaluate(() => document.body.contentEditable = "true");
await page.click("body");
const modifier = process.platform === "darwin" ? "Meta" : "Control";
await page.keyboard.down(modifier);
await page.keyboard.press("v");
await page.keyboard.up(modifier);

try {
  await page.waitForSelector("img", { timeout: 20000 });
  console.log("paste: ok");
} catch {
  console.log("paste: FAILED");
}

await browser.close();

What is the expected behavior?

The tests should not timeout.

What went wrong?

When using Puppeteer with Firefox in headless mode, navigator.clipboard.write([new ClipboardItem({ "image/png": blob })]) succeeds without error, but subsequent keyboard paste (Ctrl/Cmd+V) fails to insert the image. The same code works correctly in Chrome (headless or not) and in Firefox non-headless mode.

We should either disable these tests for Firefox in the headless mode or use #stampEditorFileInput to add the image instead, except when testing the copy/paste functionality itself.

Link to a viewer

No response

Additional context

No response