--- a/layout/style/nsCSSPseudoClassList.h
+++ b/layout/style/nsCSSPseudoClassList.h
@@ -156,17 +156,20 @@ CSS_STATE_PSEUDO_CLASS(target, ":target"
 CSS_STATE_PSEUDO_CLASS(indeterminate, ":indeterminate", 0, "",
                        NS_EVENT_STATE_INDETERMINATE)
 
 CSS_STATE_PSEUDO_CLASS(mozDevtoolsHighlighted, ":-moz-devtools-highlighted", 0, "",
                        NS_EVENT_STATE_DEVTOOLS_HIGHLIGHTED)
 
 // Matches the element which is being displayed full-screen, and
 // any containing frames.
-CSS_STATE_PSEUDO_CLASS(fullscreen, ":fullscreen", 0, "", NS_EVENT_STATE_FULL_SCREEN)
+CSS_STATE_PSEUDO_CLASS(fullscreen, ":fullscreen",
+                       CSS_PSEUDO_CLASS_ENABLED_IN_UA_SHEETS_AND_CHROME,
+                       "full-screen-api.unprefix.enabled",
+                       NS_EVENT_STATE_FULL_SCREEN)
 CSS_STATE_PSEUDO_CLASS(mozFullScreen, ":-moz-full-screen", 0, "", NS_EVENT_STATE_FULL_SCREEN)
 
 // Matches any element which is an ancestor of the DOM full-screen element,
 // or an ancestor of a containing frame of the full-screen element.
 CSS_STATE_PSEUDO_CLASS(mozFullScreenAncestor, ":-moz-full-screen-ancestor", 0, "", NS_EVENT_STATE_FULL_SCREEN_ANCESTOR)
 
 // Matches if the element is focused and should show a focus ring
 CSS_STATE_PSEUDO_CLASS(mozFocusRing, ":-moz-focusring", 0, "", NS_EVENT_STATE_FOCUSRING)