diff --git a/toolkit/modules/GMPInstallManager.jsm b/toolkit/modules/GMPInstallManager.jsm
index 0de28f769599..0fdf9eed5995 100644
--- a/toolkit/modules/GMPInstallManager.jsm
+++ b/toolkit/modules/GMPInstallManager.jsm
@@ -376,6 +376,15 @@ GMPInstallManager.prototype = {
       log.info("A version change occurred. Ignoring " +
                "media.gmp-manager.lastCheck to check immediately for " +
                "new or updated GMPs.");
+      // Firefox updated; it could be that the TrialGMPVideoDecoderCreator
+      // had failed but could now succeed, or vice versa. So reset the
+      // prefs so we re-try next time EME is used.
+      GMP_PLUGIN_IDS.concat("gmp-eme-clearkey").forEach(
+        function(id, index, array) {
+          log.info("Version change, resetting " +
+                   GMPPrefs.getPrefKey(GMPPrefs.KEY_PLUGIN_TRIAL_CREATE, id));
+          GMPPrefs.reset(GMPPrefs.KEY_PLUGIN_TRIAL_CREATE, id);
+        });
     } else {
       let secondsBetweenChecks =
         GMPPrefs.get(GMPPrefs.KEY_SECONDS_BETWEEN_CHECKS,