--- a/browser/base/content/test/general/browser_parsable_css.js
+++ b/browser/base/content/test/general/browser_parsable_css.js
@@ -43,16 +43,24 @@ let whitelist = [
    errorMessage: /Unknown property.*-moz-/i,
    isFromDevTools: false},
   // Reserved to UA sheets unless layout.css.overflow-clip-box.enabled flipped to true.
   {sourceName: /res\/forms\.css$/i,
    errorMessage: /Unknown property.*overflow-clip-box/i,
    isFromDevTools: false},
 ];
 
+if (!Services.prefs.getBoolPref("full-screen-api.unprefix.enabled")) {
+  whitelist.push({
+    sourceName: /res\/(ua|html)\.css$/i,
+    errorMessage: /Unknown pseudo-class .*\bfullscreen\b/i,
+    isFromDevTools: false
+  });
+}
+
 // Platform can be "linux", "macosx" or "win". If omitted, the exception applies to all platforms.
 let allowedImageReferences = [
   // Bug 1302691
   {file: "chrome://devtools/skin/images/dock-bottom-minimize@2x.png",
    from: "chrome://devtools/skin/toolbox.css",
    isFromDevTools: true},
   {file: "chrome://devtools/skin/images/dock-bottom-maximize@2x.png",
    from: "chrome://devtools/skin/toolbox.css",