--- a/browser/base/content/test/static/browser_parsable_css.js
+++ b/browser/base/content/test/static/browser_parsable_css.js
@@ -334,16 +334,17 @@ add_task(async function checkAllTheCSS()
   let hiddenFrame = new HiddenFrame();
   let win = await hiddenFrame.get();
   let iframe = win.document.createElementNS("http://www.w3.org/1999/xhtml", "html:iframe");
   win.document.documentElement.appendChild(iframe);
   let iframeLoaded = BrowserTestUtils.waitForEvent(iframe, "load", true);
   iframe.contentWindow.location = testFile;
   await iframeLoaded;
   let doc = iframe.contentWindow.document;
+  doc.docShell.cssErrorReportingEnabled = true;
 
   // Parse and remove all manifests from the list.
   // NOTE that this must be done before filtering out devtools paths
   // so that all chrome paths can be recorded.
   let manifestURIs = [];
   uris = uris.filter(uri => {
     if (uri.pathQueryRef.endsWith(".manifest")) {
       manifestURIs.push(uri);

--- a/layout/style/test/test_parser_diagnostics_unprintables.html
+++ b/layout/style/test/test_parser_diagnostics_unprintables.html
@@ -15,16 +15,18 @@
 <script type="application/javascript">
 // This test has intimate knowledge of how to get the CSS parser to
 // emit diagnostics that contain text under control of the user.
 // That's not the point of the test, though; the point is only that
 // *that text* is properly escaped.
 
 const isStylo = SpecialPowers.DOMWindowUtils.isStyledByServo;
 
+SpecialPowers.wrap(document).docShell.cssErrorReportingEnabled = true;
+
 // There is one "pattern" for each code path through the error reporter
 // that might need to escape some kind of user-supplied text.
 // Each "pattern" is tested once with each of the "substitution"s below:
 // <t>, <i>, and <s> are replaced by the t:, i:, and s: fields of
 // each substitution object in turn.
 let patterns = [
   // REPORT_UNEXPECTED_P (only ever used in contexts where identifier-like
   // escaping is appropriate)