diff --git a/src/display/font_loader.js b/src/display/font_loader.js
index b054f9a1f..2303a5b95 100644
--- a/src/display/font_loader.js
+++ b/src/display/font_loader.js
@@ -26,6 +26,8 @@ import { makePathFromDrawOPS } from "./display_utils.js";
 class FontLoader {
   #systemFonts = new Set();
 
+  #styleSheet = null;
+
   constructor({
     ownerDocument = globalThis.document,
     styleElement = null, // For testing only.
@@ -55,14 +57,38 @@ class FontLoader {
   }
 
   insertRule(rule) {
+    const styleSheet = this.#getStyleSheet();
+    styleSheet.insertRule(rule, styleSheet.cssRules.length);
+  }
+
+  #getStyleSheet() {
+    if (this.#styleSheet) {
+      return this.#styleSheet;
+    }
+
+    // Constructable stylesheets aren't blocked by CSP inline-style checks.
+    // Use the constructor from the document's own window, since
+    // `this._document` may belong to a different window (e.g. a print iframe)
+    // and a constructable stylesheet can only be adopted by the document it was
+    // created for.
+    const StyleSheet =
+      this._document.defaultView?.CSSStyleSheet || globalThis.CSSStyleSheet;
+    if (!this.styleElement && StyleSheet) {
+      const { adoptedStyleSheets } = this._document;
+      if (adoptedStyleSheets) {
+        const styleSheet = new StyleSheet();
+        adoptedStyleSheets.push(styleSheet);
+        return (this.#styleSheet = styleSheet);
+      }
+    }
+
     if (!this.styleElement) {
       this.styleElement = this._document.createElement("style");
       this._document.documentElement
         .getElementsByTagName("head")[0]
         .append(this.styleElement);
     }
-    const styleSheet = this.styleElement.sheet;
-    styleSheet.insertRule(rule, styleSheet.cssRules.length);
+    return (this.#styleSheet = this.styleElement.sheet);
   }
 
   clear() {
@@ -72,6 +98,16 @@ class FontLoader {
     this.nativeFontFaces.clear();
     this.#systemFonts.clear();
 
+    if (this.#styleSheet) {
+      const { adoptedStyleSheets } = this._document;
+      if (adoptedStyleSheets?.includes(this.#styleSheet)) {
+        this._document.adoptedStyleSheets = adoptedStyleSheets.filter(
+          styleSheet => styleSheet !== this.#styleSheet
+        );
+      }
+      this.#styleSheet = null;
+    }
+
     if (this.styleElement) {
       // Note: ChildNode.remove doesn't throw if the parentNode is undefined.
       this.styleElement.remove();
diff --git a/test/integration/viewer_spec.mjs b/test/integration/viewer_spec.mjs
index 9e75a59b5..feaceea1c 100644
--- a/test/integration/viewer_spec.mjs
+++ b/test/integration/viewer_spec.mjs
@@ -1973,17 +1973,14 @@ describe("PDF viewer", () => {
           null,
           {
             earlySetup: () => {
-              // Capture state while window.print() runs — the print service's
-              // destroy() removes the @page stylesheet right after, on the
-              // afterprint event.
+              // Capture state during window.print(): destroy() removes the
+              // @page stylesheet from adoptedStyleSheets right afterwards.
               window._pageRuleApplied = null;
               window.print = () => {
-                window._pageRuleApplied = [
-                  ...document.querySelectorAll("style"),
-                ].some(
+                window._pageRuleApplied = document.adoptedStyleSheets.some(
                   s =>
-                    s.sheet?.cssRules.length > 0 &&
-                    [...s.sheet.cssRules].some(r => r.cssText.includes("@page"))
+                    s.cssRules.length > 0 &&
+                    [...s.cssRules].some(r => r.cssText.includes("@page"))
                 );
               };
             },
@@ -2007,12 +2004,8 @@ describe("PDF viewer", () => {
         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.
+      // The @page rule is injected via a constructable stylesheet, which is
+      // exempt from CSP, so the strict policy in web/viewer.html applies it.
       it("must apply the injected @page rule (no CSP block)", async () => {
         await Promise.all(
           pages.map(async ([browserName, page]) => {
diff --git a/test/unit/custom_spec.js b/test/unit/custom_spec.js
index 355ded742..4c3d75918 100644
--- a/test/unit/custom_spec.js
+++ b/test/unit/custom_spec.js
@@ -14,6 +14,7 @@
  */
 
 import { buildGetDocumentParams } from "./test_utils.js";
+import { FontLoader } from "../../src/display/font_loader.js";
 import { getDocument } from "../../src/display/api.js";
 
 function getTopLeftPixel(canvasContext) {
@@ -206,4 +207,35 @@ describe("custom ownerDocument", function () {
     canvasFactory.destroy(canvasAndCtx);
     expect(style.remove.called).toBe(true);
   });
+
+  it("should use a constructable stylesheet for CSS font rules", function () {
+    const rule =
+      '@font-face {font-family:"foo";src:url(data:font/opentype;base64,AA==)}';
+
+    class MockCSSStyleSheet {
+      cssRules = [];
+
+      insertRule(cssRule, index) {
+        this.cssRules.splice(index, 0, cssRule);
+      }
+    }
+
+    const ownerDocument = {
+      adoptedStyleSheets: [],
+      defaultView: {
+        CSSStyleSheet: MockCSSStyleSheet,
+      },
+      fonts: null,
+    };
+    const fontLoader = new FontLoader({ ownerDocument });
+
+    fontLoader.insertRule(rule);
+
+    expect(ownerDocument.adoptedStyleSheets.length).toBe(1);
+    expect(ownerDocument.adoptedStyleSheets[0].cssRules).toEqual([rule]);
+
+    fontLoader.clear();
+
+    expect(ownerDocument.adoptedStyleSheets.length).toBe(0);
+  });
 });
diff --git a/web/firefox_print_service.js b/web/firefox_print_service.js
index 57e99fc7a..a993fdadf 100644
--- a/web/firefox_print_service.js
+++ b/web/firefox_print_service.js
@@ -170,9 +170,9 @@ class FirefoxPrintService {
     // Insert a @page + size rule to make sure that the page size is correctly
     // set. Note that we assume that all pages have the same size, because
     // variable-size pages are scaled down to the initial page size in Firefox.
-    this.pageStyleSheet = document.createElement("style");
-    this.pageStyleSheet.textContent = `@page { size: ${width}pt ${height}pt;}`;
-    body.append(this.pageStyleSheet);
+    this.pageStyleSheet = new CSSStyleSheet();
+    this.pageStyleSheet.replaceSync(`@page { size: ${width}pt ${height}pt;}`);
+    document.adoptedStyleSheets.push(this.pageStyleSheet);
 
     if (pdfDocument.isPureXfa) {
       getXfaHtmlForPrinting(printContainer, pdfDocument);
@@ -203,7 +203,9 @@ class FirefoxPrintService {
     body.removeAttribute("data-pdfjsprinting");
 
     if (this.pageStyleSheet) {
-      this.pageStyleSheet.remove();
+      document.adoptedStyleSheets = document.adoptedStyleSheets.filter(
+        styleSheet => styleSheet !== this.pageStyleSheet
+      );
       this.pageStyleSheet = null;
     }
   }
diff --git a/web/pdf_print_service.js b/web/pdf_print_service.js
index 8d50f0f1f..2348b7731 100644
--- a/web/pdf_print_service.js
+++ b/web/pdf_print_service.js
@@ -124,9 +124,9 @@ class PDFPrintService {
     // In browsers where @page + size is not supported, the next stylesheet
     // will be ignored and the user has to select the correct paper size in
     // the UI if wanted.
-    this.pageStyleSheet = document.createElement("style");
-    this.pageStyleSheet.textContent = `@page { size: ${width}pt ${height}pt;}`;
-    body.append(this.pageStyleSheet);
+    this.pageStyleSheet = new CSSStyleSheet();
+    this.pageStyleSheet.replaceSync(`@page { size: ${width}pt ${height}pt;}`);
+    document.adoptedStyleSheets.push(this.pageStyleSheet);
   }
 
   destroy() {
@@ -141,7 +141,9 @@ class PDFPrintService {
     body.removeAttribute("data-pdfjsprinting");
 
     if (this.pageStyleSheet) {
-      this.pageStyleSheet.remove();
+      document.adoptedStyleSheets = document.adoptedStyleSheets.filter(
+        styleSheet => styleSheet !== this.pageStyleSheet
+      );
       this.pageStyleSheet = null;
     }
     if (this._blobURLs) {
diff --git a/web/viewer-geckoview.html b/web/viewer-geckoview.html
index c9fc6d371..9cac20c70 100644
--- a/web/viewer-geckoview.html
+++ b/web/viewer-geckoview.html
@@ -26,17 +26,10 @@ 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';"
+      content="default-src 'none'; script-src resource: 'wasm-unsafe-eval'; worker-src resource:; style-src resource:; img-src resource: blob: data:; font-src resource:; connect-src resource:; base-uri 'none'; form-action 'none';"
     />-->
     <!--#endif-->
 
diff --git a/web/viewer.html b/web/viewer.html
index 66d22271a..c7e60ca86 100644
--- a/web/viewer.html
+++ b/web/viewer.html
@@ -29,33 +29,26 @@ 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-->
     <!--<link rel="icon" type="image/svg+xml" href="chrome://global/skin/icons/pdf.svg" />-->
     <!--<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';"
+      content="default-src 'none'; script-src resource: 'wasm-unsafe-eval'; worker-src resource:; style-src resource:; 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';"
+      content="default-src 'none'; script-src 'self' 'wasm-unsafe-eval' 'unsafe-eval'; worker-src 'self' blob:; style-src 'self'; 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 * file: chrome-extension: blob: data: filesystem: drive:; base-uri 'self'; form-action 'none';"
+      content="default-src 'none'; script-src 'self' 'wasm-unsafe-eval'; worker-src 'self' blob:; style-src 'self'; img-src 'self' blob: data:; font-src 'self' data:; connect-src * file: chrome-extension: blob: data: filesystem: drive:; 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';"
+      content="default-src 'none'; script-src 'self' 'wasm-unsafe-eval'; worker-src 'self' blob:; style-src 'self'; img-src 'self' blob: data:; font-src 'self' data:; connect-src * blob: data:; base-uri 'none'; form-action 'none';"
     />-->
     <!--#endif-->