diff --git a/browser/base/content/browser.css b/browser/base/content/browser.css
index 9075ea02acf0..f5aad31f2aa0 100644
--- a/browser/base/content/browser.css
+++ b/browser/base/content/browser.css
@@ -252,6 +252,11 @@ toolbar[customizing] > .overflow-button {
 
 %endif
 
+#main-window[inFullscreen] #global-notificationbox,
+#main-window[inFullscreen] #high-priority-global-notificationbox {
+  visibility: collapse;
+}
+
 /* Rules to help integrate SDK widgets */
 toolbaritem[sdkstylewidget="true"] > toolbarbutton,
 toolbarpaletteitem > toolbaritem[sdkstylewidget="true"] > iframe,