diff --git a/companion/wxt.config.ts b/companion/wxt.config.ts
index 5bd7a4eabb..81e632a325 100644
--- a/companion/wxt.config.ts
+++ b/companion/wxt.config.ts
@@ -46,6 +46,9 @@ export default defineConfig({
     "build:manifestGenerated": (_wxt, manifest) => {
       manifest.browser_specific_settings ??= {};
       manifest.browser_specific_settings.gecko ??= {};
+      // Stable extension ID for Firefox development - ensures consistent OAuth redirect URL
+      // This must be an email-like string for Firefox to accept it
+      manifest.browser_specific_settings.gecko.id = "companion@cal.com";
       manifest.browser_specific_settings.gecko.data_collection_permissions = {
         required: ["none"],
       };