diff --git a/js/mediaLibrariesOverrides.js b/js/mediaLibrariesOverrides.js
index d9cdef2..56ee0fc 100644
--- a/js/mediaLibrariesOverrides.js
+++ b/js/mediaLibrariesOverrides.js
@@ -181,6 +181,35 @@ window.mejs.MediaElementPlayer.prototype.setTrack = function (lang) {
 
 };
 
+/**
+ * Fix for firefox fullscreen api
+ * https://github.com/adaptlearning/adapt-contrib-media/issues/239
+ */
+const mediaFeatures = window.mejs.MediaFeatures;
+if (mediaFeatures.hasMozNativeFullScreen) {
+  Object.assign(mediaFeatures, {
+    fullScreenEventName: document.exitFullscreen
+      ? 'fullscreenchange'
+      : 'mozfullscreenchange',
+    requestFullScreen: el => {
+      document.exitFullscreen
+        ? el.requestFullscreen()
+        : el.mozRequestFullScreen();
+    },
+    isFullScreen: () => {
+      return document.exitFullscreen
+        ? Boolean(document.fullscreenElement)
+        : document.mozFullScreen;
+    },
+    cancelFullScreen: el => {
+      if (!mediaFeatures.isFullScreen()) return;
+      document.exitFullscreen
+        ? document.exitFullscreen()
+        : document.mozCancelFullScreen();
+    }
+  });
+}
+
 /**
  * Overwrite mediaelement-and-player enterFullScreen to remove Chrome <17 bug fix (Media issue #255)
 */