diff --git a/gulpfile.mjs b/gulpfile.mjs
index 1b9481152..cebe49e5c 100644
--- a/gulpfile.mjs
+++ b/gulpfile.mjs
@@ -1209,6 +1209,10 @@ function discardCommentsCSS() {
 }
 
 function preprocessHTML(source, defines) {
+  defines = {
+    ...defines,
+    TESTING: defines.TESTING ?? process.env.TESTING === "true",
+  };
   const outName = getTempFile("~preprocess", ".html");
   preprocess(source, outName, defines);
   const out = fs.readFileSync(outName).toString();
diff --git a/test/integration/viewer_spec.mjs b/test/integration/viewer_spec.mjs
index deb059ef1..1309029a9 100644
--- a/test/integration/viewer_spec.mjs
+++ b/test/integration/viewer_spec.mjs
@@ -26,8 +26,11 @@ import {
   waitForPageChanging,
   waitForPageRendered,
 } from "./test_utils.mjs";
+import path from "path";
 import { PNG } from "pngjs";
 
+const __dirname = import.meta.dirname;
+
 describe("PDF viewer", () => {
   describe("Zoom origin", () => {
     let pages;
@@ -1892,5 +1895,108 @@ describe("PDF viewer", () => {
         );
       });
     });
+
+    describe("@page size stylesheet under CSP", () => {
+      let pages;
+
+      beforeEach(async () => {
+        pages = await loadAndWait(
+          "basicapi.pdf",
+          ".textLayer .endOfContent",
+          null,
+          {
+            earlySetup: () => {
+              // Capture state while window.print() runs — the print service's
+              // destroy() removes the @page stylesheet right after, on the
+              // afterprint event.
+              window._pageRuleApplied = null;
+              window.print = () => {
+                window._pageRuleApplied = [
+                  ...document.querySelectorAll("style"),
+                ].some(
+                  s =>
+                    s.sheet?.cssRules.length > 0 &&
+                    [...s.sheet.cssRules].some(r => r.cssText.includes("@page"))
+                );
+              };
+            },
+            appSetup: app => {
+              app._testPrintResolver = Promise.withResolvers();
+            },
+            eventBusSetup: eventBus => {
+              eventBus.on(
+                "afterprint",
+                () => {
+                  window.PDFViewerApplication._testPrintResolver.resolve();
+                },
+                { once: true }
+              );
+            },
+          }
+        );
+      });
+
+      afterEach(async () => {
+        await closePages(pages);
+      });
+
+      // The print service injects an inline
+      // <style>@page { size: WxH pt }</style> to match the PDF's page
+      // dimensions. If the CSP `style-src-elem` directive blocks inline
+      // <style> elements, the element is created but its content is never
+      // parsed — `sheet.cssRules` stays empty and the @page rule has no
+      // effect. See web/viewer.html.
+      it("must apply the injected @page rule (no CSP block)", async () => {
+        await Promise.all(
+          pages.map(async ([browserName, page]) => {
+            await waitAndClick(page, "#printButton");
+            await awaitPromise(
+              await page.evaluateHandle(() => [
+                window.PDFViewerApplication._testPrintResolver.promise,
+              ])
+            );
+
+            const hasPageRule = await page.evaluate(
+              () => window._pageRuleApplied
+            );
+            expect(hasPageRule)
+              .withContext(
+                `In ${browserName}: injected @page stylesheet was parsed`
+              )
+              .toBeTrue();
+          })
+        );
+      });
+    });
+  });
+
+  describe("Open a new PDF via the file input", () => {
+    let pages;
+
+    beforeEach(async () => {
+      pages = await loadAndWait("tracemonkey.pdf", ".textLayer .endOfContent");
+    });
+
+    afterEach(async () => {
+      await closePages(pages);
+    });
+
+    // The "Open" input wraps the chosen file in a blob URL,
+    // which the worker then fetches. `connect-src` in the production CSP must
+    // therefore allow `blob:` — see web/viewer.html.
+    it("must load a PDF picked through the file input (blob URL)", async () => {
+      await Promise.all(
+        pages.map(async ([browserName, page]) => {
+          const fileInput = await page.$("#fileInput");
+          await fileInput.uploadFile(
+            path.join(__dirname, "../pdfs/basicapi.pdf")
+          );
+
+          await page.waitForFunction(
+            () => window.PDFViewerApplication.pdfDocument?.numPages === 3
+          );
+        })
+      );
+    });
   });
 });
diff --git a/web/viewer-geckoview.html b/web/viewer-geckoview.html
index daa468bc2..c9fc6d371 100644
--- a/web/viewer-geckoview.html
+++ b/web/viewer-geckoview.html
@@ -26,6 +26,20 @@ See https://github.com/adobe-type-tools/cmap-resources
     <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1" />
     <title>PDF.js viewer</title>
 
+    <!--
+      The print service injects an inline <style>@page { size: … }</style>
+      at print time (web/pdf_print_service.js, web/firefox_print_service.js)
+      to match the PDF's page dimensions. Since the size varies per PDF the
+      content can't be pre-hashed, so style-src-elem allows 'unsafe-inline'.
+      Inline style="…" attributes stay blocked via style-src (no fallback).
+    -->
+    <!--#if MOZCENTRAL-->
+    <!--<meta
+      http-equiv="Content-Security-Policy"
+      content="default-src 'none'; script-src resource: 'wasm-unsafe-eval'; worker-src resource:; style-src resource:; style-src-elem resource: 'unsafe-inline'; img-src resource: blob: data:; font-src resource:; connect-src resource:; base-uri 'none'; form-action 'none';"
+    />-->
+    <!--#endif-->
+
     <!--#if MOZCENTRAL-->
     <!--#include viewer-snippet-firefox-extension.html-->
     <!--#endif-->
diff --git a/web/viewer-snippet-chrome-overlays.html b/web/viewer-snippet-chrome-overlays.html
index fff0eb2f3..357b85107 100644
--- a/web/viewer-snippet-chrome-overlays.html
+++ b/web/viewer-snippet-chrome-overlays.html
@@ -4,19 +4,7 @@
          users with recognizing which checkbox they have to click when they
          visit chrome://extensions.
     -->
-    <p
-      id="chrome-pdfjs-logo-bg"
-      style="
-        display: block;
-        padding-left: 60px;
-        min-height: 48px;
-        background-size: 48px;
-        background-repeat: no-repeat;
-        font-size: 14px;
-        line-height: 1.8em;
-        word-break: break-all;
-      "
-    >
+    <p id="chrome-pdfjs-logo-bg">
       Click on "<span id="chrome-file-access-label">Allow access to file URLs</span>" at
       <a id="chrome-link-to-extensions-page">chrome://extensions</a>
       <br />
diff --git a/web/viewer.css b/web/viewer.css
index 832439af4..4defccd10 100644
--- a/web/viewer.css
+++ b/web/viewer.css
@@ -713,6 +713,25 @@ dialog :link {
   margin-top: 10px;
 }
 
+/*#if !MOZCENTRAL*/
+#printServiceDialog {
+  min-width: 200px;
+}
+/*#endif*/
+
+/*#if CHROME*/
+#chrome-pdfjs-logo-bg {
+  display: block;
+  padding-left: 60px;
+  min-height: 48px;
+  background-size: 48px;
+  background-repeat: no-repeat;
+  font-size: 14px;
+  line-height: 1.8em;
+  word-break: break-all;
+}
+/*#endif*/
+
 .grab-to-pan-grab {
   cursor: grab !important;
 }
diff --git a/web/viewer.html b/web/viewer.html
index 0d5d90c7d..e4d24d7e4 100644
--- a/web/viewer.html
+++ b/web/viewer.html
@@ -29,6 +29,35 @@ See https://github.com/adobe-type-tools/cmap-resources
     <!--#endif-->
     <title>PDF.js viewer</title>
 
+    <!--
+      The print service injects an inline <style>@page { size: … }</style>
+      at print time (web/pdf_print_service.js, web/firefox_print_service.js)
+      to match the PDF's page dimensions. Since the size varies per PDF the
+      content can't be pre-hashed, so style-src-elem allows 'unsafe-inline'.
+      Inline style="…" attributes stay blocked via style-src (no fallback).
+    -->
+    <!--#if MOZCENTRAL-->
+    <!--<meta
+      http-equiv="Content-Security-Policy"
+      content="default-src 'none'; script-src resource: 'wasm-unsafe-eval'; worker-src resource:; style-src resource:; style-src-elem resource: 'unsafe-inline'; img-src resource: blob: data:; font-src resource:; connect-src resource:; base-uri 'none'; form-action 'none';"
+    />-->
+    <!--#elif TESTING-->
+    <!--<meta
+      http-equiv="Content-Security-Policy"
+      content="default-src 'none'; script-src 'self' 'wasm-unsafe-eval' 'unsafe-eval'; worker-src 'self' blob:; style-src 'self'; style-src-elem 'self' 'unsafe-inline'; img-src 'self' blob: data:; font-src 'self' data:; connect-src * blob: data:; base-uri 'self'; form-action 'none';"
+    />-->
+    <!--#elif CHROME-->
+    <!--<meta
+      http-equiv="Content-Security-Policy"
+      content="default-src 'none'; script-src 'self' 'wasm-unsafe-eval'; worker-src 'self' blob:; style-src 'self'; style-src-elem 'self' 'unsafe-inline'; img-src 'self' blob: data:; font-src 'self' data:; connect-src * blob: data:; base-uri 'self'; form-action 'none';"
+    />-->
+    <!--#else-->
+    <!--<meta
+      http-equiv="Content-Security-Policy"
+      content="default-src 'none'; script-src 'self' 'wasm-unsafe-eval'; worker-src 'self' blob:; style-src 'self'; style-src-elem 'self' 'unsafe-inline'; img-src 'self' blob: data:; font-src 'self' data:; connect-src * blob: data:; base-uri 'none'; form-action 'none';"
+    />-->
+    <!--#endif-->
+
     <!--#if MOZCENTRAL-->
     <!--#include viewer-snippet-firefox-extension.html-->
     <!--#elif CHROME-->
@@ -1237,7 +1266,7 @@ See https://github.com/adobe-type-tools/cmap-resources
         </dialog>
 
         <!--#if !MOZCENTRAL-->
-        <dialog id="printServiceDialog" style="min-width: 200px">
+        <dialog id="printServiceDialog">
           <div class="row">
             <span data-l10n-id="pdfjs-print-progress-message"></span>
           </div>