diff --git a/platform/firefox/vapi-background-ext.js b/platform/firefox/vapi-background-ext.js
index 66f126132..bcca2440a 100644
--- a/platform/firefox/vapi-background-ext.js
+++ b/platform/firefox/vapi-background-ext.js
@@ -307,7 +307,7 @@ vAPI.Net = class extends vAPI.Net {
 vAPI.scriptletsInjector = ((doc, scriptlets) => {
     let script, url;
     try {
-        const blob = new self.Blob([ scriptlets ], { type: 'text/javascript' });
+        const blob = new self.Blob([ scriptlets ], { type: 'text/javascript; charset=utf-8' });
         url = self.URL.createObjectURL(blob);
         script = doc.createElement('script');
         script.async = false;